Terms such as "functional colonic disease" (or "functional bowel disorder") refer in medicine to a group of bowel disorders which are characterised by chronic abdominal complaints without a structural or biochemical cause that could explain symptoms. Other "functional" disorders relate to other aspects of the process of digestion.

The consensus review process of meetings and publications organised by the Rome Foundation, known as the Rome process, has helped to define the functional gastrointestinal disorders. Successively, the Rome I, Rome II, Rome III and Rome IV proposed consensual classification system and terminology, as recommended by the Rome Coordinating Committee. These now include classifications appropriate for adults, children and neonates / toddlers.

The current Rome IV classification, published in 2016, is as follows:

A. Esophageal Disorders

- A1. Functional chest pain

- A2. Functional heartburn

- A3. Reflux hypersensitivity

- A4. Globus

- A5. Functional dysphagia

B. Gastroduodenal Disorders

- B1. Functional dyspepsia

- B1a. Postprandial distress syndrome (PDS)

- B1b. Epigastric pain syndrome (EPS)

- B2. Belching disorders

- B2a. Excessive supragastric belching

- B2b. Excessive gastric belching

- B3. Nausea and vomiting disorders

- B3a. Chronic nausea vomiting syndrome (CNVS}

- B3b. Cyclic vomiting syndrome (CVS)

- B3c. Cannabinoid hyperemesis syndrome (CHS)

- B4. Rumination syndrome

C. Bowel Disorders

- C1. Irritable bowel syndrome (IBS)

- IBS with predominant constipation (IBS-C)

- IBS with predominant diarrhea (IBS-D)

- IBS with mixed bowel habits (IBS-M)

- IBS unclassified (IBS-U)

- C2. Functional constipation

- C3. Functional diarrhea

- C4. Functional abdominal bloating/distension

- C5. Unspecified functional bowel disorder

- C6. Opioid-induced constipation

D. Centrally Mediated Disorders of Gastrointestinal Pain

- D1. Centrally mediated abdominal pain syndrome (CAPS)

- D2. Narcotic bowel syndrome (NBS)/ Opioid-induced GI hyperalgesia

E. Gallbladder and Sphincter of Oddi disorders

- E1. Biliary pain

- E1a. Functional gallbladder disorder

- E1b. Functional biliary sphincter of Oddi disorder

- E2. Functional pancreatic sphincter of Oddi disorder

F. Anorectal Disorders

- F1. Fecal incontinence

- F2. Functional anorectal pain

- F2a. Levator ani syndrome

- F2b. Unspecified functional anorectal pain

- F2c. Proctalgia fugax

- F3. Functional defecation disorders

- F3a. Inadequate defecatory propulsion

- F3b. Dyssynergic defecation

G. Childhood Functional GI Disorders: Neonate/Toddler

- G1. Infant regurgitation

- G2. Rumination syndrome

- G3. Cyclic vomiting syndrome (CVS)

- G4. Infant colic

- G5. Functional diarrhea

- G6. Infant dyschezia

- G7. Functional constipation

H. Childhood Functional GI Disorders: Child/Adolescent

- H1. Functional nausea and vomiting disorders

- H1a. Cyclic vomiting syndrome (CVS)

- H1b. Functional nausea and functional vomiting

- H1b1. Functional nausea

- H1b2. Functional vomiting

- H1c. Rumination syndrome

- H1d. Aerophagia

- H2. Functional abdominal pain disorders

- H2a. Functional dyspepsia

- H2a1. Postprandial distress syndrome

- H2a2. Epigastric pain syndrome

- H2b. Irritable bowel syndrome (IBS)

- H2c. Abdominal migraine

- H2d. Functional abdominal pain ‒ NOS

- H3. Functional defecation disorders

- H3a. Functional constipation

- H3b. Nonretentive fecal incontinence

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.