Small angiomyolipomas and those without dilated blood vessels (aneurysms) cause few problems, but angiomyolipomas have been known to grow as rapidly as 4 cm in one year. An angiomyolipoma larger than 5 cm and those containing an aneurysm pose a significant risk of rupture, which is a medical emergency as it is potentially life-threatening. One population study found the cumulative risk of haemorrhage to be 10% in males and 20% in females.

A second problem occurs when the renal angiomyolipomas take over so much kidney that the function is impaired leading to chronic kidney disease. This may be severe enough to require dialysis. A population survey of patients with TSC and normal intelligence found 1% were on dialysis.

Angiomyolipomas are the most common benign tumour of the kidney and are found either in patients with tuberous sclerosis or sporadically. About 80–90% of cases are sporadic and these are most commonly found in middle-aged women.

In patients with TSC, a longitudinal study found 80% will have some form of renal lesion by around 10 years of age. Of these, 75% are angiomyolipomas and 17% cysts. The angiomyolipomas increased in size in around 60% of these children. An autopsy study and TSC clinic survey found a prevalence of 67% and 85% respectively for patients with TSC. Both genders are affected equally.

2004 research showed that CCSK patients exhibit an improved relapse-free survival from a longer course of therapy when using vincristine, doxorubicin, and dactinomycin, but their long-term survival is unchanged compared with patients receiving 6 months of therapy.

Kidney tumours may be discovered on medical imaging incidentally (i.e. an incidentaloma), or may be present in patients as an abdominal mass or kidney cyst, hematuria, abdominal pain, or manifest first in a paraneoplastic syndrome that seems unrelated to the kidney.

Kidney tumours (or kidney tumors), also known as renal tumours, are tumours, or growths, on or in the kidney. These growths can be benign or malignant (kidney cancer).

Clear cell sarcoma of the kidney (CCSK) is an extremely rare type of kidney cancer comprising 3% of all pediatric renal tumours. Clear cell sarcoma of the kidney can spread from the kidney to other organs, most commonly the bone, but also including the lungs, brain, and soft tissues of the body.

Despite the similarities in names, "clear cell sarcoma of the kidney" is unrelated to clear cell sarcoma of soft tissue, also known as malignant melanoma of soft parts.

The United States' NIH estimates for 2013 around 64,770 new cases of kidney cancer and 13,570 deaths from the disease.

The incidence of kidney cancer is also increasing in the United States. This is thought to be a real increase, not only due to changes in the way the disease is diagnosed.

The most recent estimates of incidence of kidney cancer suggest that there are 63,300 new cases annually in the EU25. In Europe, kidney cancer accounts for nearly 3% of all cancer cases.

To minimize the risk for contrast-induced nephropathy, various actions can be taken if the patient has predisposing conditions. These have been reviewed in a meta-analysis. A separate meta-analysis addresses interventions for emergency patients with baseline insufficient kidney function.

Individuals with chronic kidney disease, diabetes mellitus, high blood pressure, reduced intravascular volume, or who are elderly are at increased risk of developing CIN after exposure to iodinated contrast.

A clinical prediction rule is available to estimate probability of nephropathy (increase ≥25% and/or ≥0.5 mg/dl in serum creatinine at 48 h):

Risk Factors:

- Systolic blood pressure <80 mm Hg - 5 points

- Intraarterial balloon pump - 5 points

- Congestive heart failure (Class III-IV or history of pulmonary edema) - 5 points

- Age >75 y - 4 points

- Hematocrit level <39% for men and <35% for women - 3 points

- Diabetes mellitus- 3 points

- Contrast media volume - 1 point for each 100 mL

- Decreased kidney function:

- Serum creatinine level >1.5 g/dL - 4 points

- Estimated Glomerular filtration rate (online calculator)

Scoring:

5 or less points

- Risk of CIN - 7.5

- Risk of Dialysis - 0.04%

6–10 points

- Risk of CIN - 14.0

- Risk of Dialysis - 0.12%

11–16 points

- Risk of CIN - 26.1*

- Risk of Dialysis - 1.09%

>16 points

- Risk of CIN - 57.3

- Risk of Dialysis - 12.8%

The evidence linking vitamin C supplements with an increased rate of kidney stones is inconclusive. The excess dietary intake of vitamin C might increase the risk of calcium oxalate stone formation, in practice this is rarely encountered. The link between vitamin D intake and kidney stones is also tenuous. Excessive vitamin D supplementation may increase the risk of stone formation by increasing the intestinal absorption of calcium; correction of a deficiency does not.

In ADPKD patients, gradual cyst development and expansion result in kidney enlargement, and during the course of the disease, glomerular filtration rate (GFR) remains normal for decades before kidney function starts to progressively deteriorate, making early prediction of renal outcome difficult. The CRISP study, mentioned in the treatment section above, contributed to build a strong rationale supporting the prognostic value of total kidney volume (TKV) in ADPKD; TKV (evaluated by MRI) increases steadily and a higher rate of kidney enlargement correlated with accelerated decline of GFR, while patient height-adjusted TKV (HtTKV) ≥600 ml/m predicts the development of stage 3 chronic kidney disease within 8 years.

Besides TKV and HtTKV, the estimated glomerular filtration rate (eGFR) has also been tentatively used to predict the progression of ADPKD. After the analysis of CT or MRI scans of 590 patients with ADPKD treated at the Mayo Translational Polycystic Kidney Disease Center, Irazabal and colleagues developed an imaging-based classification system to predict the rate of eGFR decline in patients with ADPKD. In this prognostic method, patients are divided into five subclasses of estimated kidney growth rates according to age-specific HtTKV ranges (1A, 6.0%) as delineated in the CRISP study. The decline in eGFR over the years following initial TKV measurement is significantly different between all five patient subclasses, with those in subclass 1E having the most rapid decline.

There are no conclusive data demonstrating a cause-and-effect relationship between alcoholic beverage consumption and kidney stones. However, some have theorized that certain behaviors associated with frequent and binge drinking can lead to dehydration, which can, in turn, lead to the development of kidney stones.

The American Urological Association has projected that global warming will lead to an increased incidence of kidney stones in the United States by expanding the "kidney stone belt" of the southern United States.

People with lymphoproliferative/myeloproliferative disorders who were treated with chemotherapy developed symptomatic kidney stones 1.8% of the time in one study.

In the general population, the frequency of medullary sponge kidney disease is reported to be 0.02–0.005%; that is, 1 in 5000 to 1 in 20,000. The frequency of medullary sponge kidney has been reported by various authors to be 1221% in patients with kidney stones. The disease is bilateral in 70% of cases.

Overall, most people with thin basement membrane disease have an excellent prognosis. Some reports, however, suggest that a minority might develop hypertension.

Thin basement membrane disease may co-exist with other kidney diseases, which may in part be explained by the high prevalence of thin basement membrane disease.

It is accepted that kidney transplantation is the preferred treatment for ADPKD patients with end-stage renal disease (ESRD). Among American patients on the kidney transplant waiting list (as of December 2011), 7256 (8.4%) were listed due to cystic kidney disease and of the 16,055 renal transplants performed in 2011, 2057 (12.8%) were done for patients with cystic kidney disease, with 1,189 from deceased donors and 868 from living donors.

While most cases of horseshoe kidneys are asymptomatic and discovered upon autopsy, the condition may increase the risk for:

- Kidney obstruction – abnormal placement of ureter may lead to obstruction and dilation of the kidney.

- Kidney infections – associated with vesicoureteral reflux.

- Kidney stones – deviant orientation of kidneys combined with slow urine flow and kidney obstruction may lead to kidney stones.

- Kidney cancer – increased risk of renal cancer, especially Wilms' tumor, transitional cell carcinoma, and an occasional case report of carcinoid tumor. Despite increased risk, the overall risk is still relatively low.

The prevalence of horseshoe kidneys in females with Turner Syndrome is about 15%.

It can be associated with trisomy 18.

It can be associated with venous anomalies like left sided IVC 9.

In regard to the epidemiology of multicystic dysplasia kidney, the incidence of MCDK is estimated to be 1 in every 4,000 live births, making it rare in terms of the general population.

Many forms of cystic kidney disease can be detected in children prior to birth. Abnormalities which only affect one kidney are unlikely to cause a problem with the healthy arrival of a baby. Abnormalities which affect both kidneys can have an effect on the baby's amniotic fluid volume which can in turn lead to problems with lung development. Some forms of obstruction can be very hard to differentiate from cystic renal disease on early scans.

Patients with ESKD are at increased overall risk for cancer. This risk is particularly high in younger patients and gradually diminishes with age. Medical specialty professional organizations recommend that physicians do not perform routine cancer screening in patients with limited life expectancies due to ESKD because evidence does not show that such tests lead to improved patient outcomes.

The osmolality of the contrast agent was previously believed to be an important factor in contrast-induced nephropathy. Today it has become increasingly clear that other physicochemical properties play a greater role, such as viscosity. Attention should be paid to using contrast agents of low viscosity. Moreover, sufficient fluids should be supplied to limit fluid viscosity of urine. Modern iodinated contrast agents are non-ionic, the older ionic types caused more adverse effects, and their use has diminished.

Epidemiologically speaking, nephronophthisis, occurs equally in both sexes, and has an estimate 9 in about 8 million rate in individuals. Nephronophthisis is the leading monogenic cause of end-stage renal disease.

Congenital mesoblastic nephroma, while rare, is the most common kidney neoplasm diagnosed in the first three months of life and accounts for 3-5% of all childhood renal neoplasms. This neoplasm is generally non-aggressive and amenable to surgical removal. However, a readily identifiable subset of these kidney tumors has a more malignant potential and is capable of causing life-threatening metastases. Congenital mesoblastic nephroma was first named as such in 1967 but was recognized decades before this as fetal renal hamartoma or leiomyomatous renal hamartoma.

The cause of multicystic dysplastic kidney can be attributed to genetics. Renal dysplasia can be a consequence of a genetic syndrome, which in turn may affect the digestive tract, nervous system, or other areas of the urinary tract. If the mother had been taking certain prescription drugs such as those for hypertension, this may be a precipitating factor as well.

The "APOL1" gene has been proposed as a major genetic risk locus for a spectrum of nondiabetic renal failure in individuals of African origin, these include HIV-associated nephropathy (HIVAN), primary nonmonogenic forms of focal segmental glomerulosclerosis, and hypertension affiliated chronic kidney disease not attributed to other etiologies. Two western African variants in APOL1 have been shown to be associated with end stage kidney disease in African Americans and Hispanic Americans.

Complications associated with medullary sponge kidney include the following:

- Kidney stones

- Urinary tract infection (UTI)

- Blood in the urine

- Distal renal tubular acidosis (Type 1 RTA)

- Chronic kidney disease (rarely)

- Marked chronic pain