Ulcerative colitis (UC) is a lifelong relapsing–remitting disease with no reliable medical cure; proctocolectomy is the only definitive cure.^[1] In population-based cohorts, the cumulative risk of relapse is approximately 70–80% at 10 years, about 10–15% of patients follow an aggressive course, nearly half require at least one UC-related hospitalization, and the 5- and 10-year cumulative risk of colectomy is approximately 10–15%.^[2] Major complications include acute severe ulcerative colitis with toxic megacolon, perforation or massive hemorrhage, venous thromboembolism, extraintestinal manifestations, and colitis-associated colorectal cancer (CRC).^[3] Contemporary CRC risk is substantially lower than historical referral-center estimates, and surveillance colonoscopy is risk-stratified, beginning 8 years after symptom onset or at diagnosis of primary sclerosing cholangitis (PSC).^[4][5] Large nationwide cohorts show a modest excess all-cause mortality (adjusted HR ~1.4 in Sweden), although relative mortality has declined over time.^[6]

• Left-sided colitis is the most frequent distribution at diagnosis.^[2] Across population-based cohorts, 30–60% present with proctitis, 16–45% with left-sided colitis, and 14–35% with extensive colitis.^[1]
• Proximal extension occurs in 10–30% of patients over time, approximately 10–19% at 5 years and 11–28% at 10 years.^[2][7]
• Fewer than 5% of patients are later reclassified as Crohn’s disease.^[1][2]

• Most patients have a mild-to-moderate course that is most active at diagnosis, followed by variable periods of remission or mild activity.^[2]
• Cumulative relapse risk is approximately 70–80% at 10 years; about 10–15% of patients experience an aggressive course.^[2]
• UC is increasingly regarded as a progressive disease: persistent inflammation is associated with phenotypic extension, structural bowel damage, colorectal dysfunction, neoplasia, hospitalization, and colectomy.^[8]

• Younger age at onset (<40 years); onset after age 60 tends to be milder^[1]
• Extensive colitis
• Deep ulcerations and failure to achieve mucosal healing
• High perinuclear antineutrophil cytoplasmic antibody (pANCA) titers
• Fever or weight loss at diagnosis, short interval to first flare, and active disease in the preceding year^[9]

• Almost 50% of patients require UC-related hospitalization, and the 5-year risk of re-hospitalization is ~50%.^[2]
• Within 5 years of diagnosis, ~20% of patients are hospitalized and ~7% undergo colectomy.^[4]
• The 5- and 10-year cumulative colectomy risk is ~10–15%; older estimates of 20–40% reflect pre-biologic, referral-center populations. Achieving mucosal healing is associated with a lower colectomy risk.^[2]

• Acute severe ulcerative colitis may be complicated by toxic megacolon (nonobstructive colonic dilatation, classically of the transverse colon, with systemic toxicity), bowel perforation, and massive hemorrhage.^[3][10]
• Venous thromboembolism risk is increased, particularly during active disease and hospitalization.^[3]

• Structural damage: benign strictures, pseudopolyps, a shortened ahaustral (“lead-pipe”) colon, colonic dysmotility, and anorectal dysfunction.^[1][8]
• Hematologic: iron deficiency anemia and anemia of chronic disease.^[3]
• Neoplasia: dysplasia and colitis-associated CRC (see below).

Extraintestinal manifestations (EIMs) are common; one review estimated EIMs, including PSC, in approximately 27% of patients with UC.^[4]

• Musculoskeletal: peripheral arthropathy, sacroiliitis, ankylosing spondylitis
• Cutaneous: erythema nodosum, pyoderma gangrenosum
• Ocular: episcleritis, uveitis
• Hepatobiliary: primary sclerosing cholangitis
• Oral: aphthous ulcers^[3]

• UC confers approximately a 1.7-fold higher CRC risk than the general population, with a cumulative risk of ~4.5% at 20 years.^[4]
• Contemporary cumulative estimates (~1%, ~3%, and ~7% at 10, 20, and 30 years) are substantially lower than the classic referral-center estimates (2%, 8%, and 18%).^[10]
• In population-based cohorts, ~1.5% of patients were diagnosed with CRC after 15 years of follow-up.^[2]
• Isolated proctitis carries little or no excess risk.^[11]

• Longer disease duration and greater anatomic extent
• Cumulative inflammatory burden (severity and persistence of endoscopic/histologic inflammation), an independent and modifiable risk factor^[8]
• Concomitant PSC
• Family history of CRC, especially a first-degree relative diagnosed before age 50
• Colonic stricture, dense pseudopolyposis, prior dysplasia, and a tubular/shortened colon^[12][5]

• PSC occurs in a minority of patients with UC, whereas most patients with PSC have inflammatory bowel disease, most commonly UC; the association is bidirectional.^[13][4]
• PSC-associated UC is a distinct phenotype: often extensive but endoscopically mild colitis with right-sided predominance, rectal sparing, and backwash ileitis.^[1]
• CRC risk is approximately 4-fold higher in UC with PSC than in UC alone.^[14]
• Long-term outcome in PSC-UC is driven largely by hepatobiliary disease, including end-stage liver disease, cholangiocarcinoma, and need for liver transplantation.^[13]
• Whether colectomy modifies PSC progression or post-transplant recurrence is uncertain; observational data conflict, and colectomy decisions are driven by colonic indications.^[13]

• A meta-analysis of population-based inception cohorts found no significant excess overall mortality but increased mortality from gastrointestinal causes.^[15]
• Larger nationwide cohorts show a modest excess: in Sweden, all-cause mortality in UC was increased (HR ~1.4), relative mortality declined over time, and incident IBD cases diagnosed 2002–2014 had an estimated life span 2.3 years shorter than matched comparators.^[6] UK primary-care data also show increased mortality in IBD compared with matched controls.^[16]
• Individuals with UC have a lower life expectancy than the general population.^[4]

• Chronic diarrhea, rectal bleeding, fatigue, and work disability substantially impair quality of life even when survival is near-normal.^[4][2]

• Proctitis and limited left-sided disease carry a comparatively benign course and little excess CRC risk; extensive colitis, young onset, and PSC mark higher-risk phenotypes.^[1][11]
• Mucosal healing is associated with lower colectomy risk, and reducing cumulative inflammatory burden lowers neoplasia risk.^[2][8]