Signs and symptoms of acute pyelonephritis generally develop rapidly over a few hours or a day. It can cause high fever, pain on passing urine, and abdominal pain that radiates along the flank towards the back. There is often associated vomiting.

Chronic pyelonephritis causes persistent flank or abdominal pain, signs of infection (fever, unintentional weight loss, malaise, decreased appetite), lower urinary tract symptoms and blood in the urine. Chronic pyelonephritis can in addition cause fever of unknown origin. Furthermore, inflammation-related proteins can accumulate in organs and cause the condition AA amyloidosis.

Physical examination may reveal fever and tenderness at the costovertebral angle on the affected side.

Pyelonephritis that has progressed to urosepsis may be accompanied by signs of septic shock, including rapid breathing, decreased blood pressure, shivering, and occasionally delirium.

Pyelonephritis is inflammation of the kidney, typically due to a bacterial infection. Symptoms most often include fever and flank tenderness. Other symptoms may include nausea, burning with urination, and frequent urination. Complications may include pus around the kidney, sepsis, or kidney failure.

It is typically due to a bacterial infection, most commonly "Escherichia coli". Risk factors include sexual intercourse, prior urinary tract infections, diabetes, structural problems of the urinary tract, and spermicide use. The mechanism of infection is usually spread up the urinary tract. Less often infection occurs through the bloodstream. Diagnosis is typically based on symptoms and supported by urinalysis. If there is no improvement with treatment, medical imaging may be recommended.

Pyelonephritis may be preventable by urination after sex and drinking sufficient fluids. Once present it is generally treatment with antibiotic, such as ciprofloxacin or ceftriaxone. Those with severe disease may required treatment in hospital. In those with certain structural problems of the urinary tract or kidney stones, surgery may be required.

Pyelonephritis is common. About 1 to 2 per 1,000 women are affected a year and just under 0.5 per 1,000 males. Young adult females are most often affected, followed by the very young and old. With treatment, outcomes are generally good in young adults. Among people over the age of 65 the risk of death is about 40%.