Ulcerative colitis is a chronic disease with recurrent symptoms and significant morbidity. The precise etiology is still unknown. As many as 25 percent of patients with ulcerative colitis have extraintestinal manifestations. The diagnosis is made endoscopically. Tests such as perinuclear antineutrophilic cytoplasmic antibodies and anti-Saccharomyces cerevisiae antibodies are promising, but not yet recommended for routine use. Treatment is based on the extent and severity of the disease. Rectal therapy with 5-aminosalicylic acid compounds is used for proctitis. More extensive disease requires treatment with oral 5-aminosalicylic acid compounds and oral corticosteroids. The side effects of steroids limit their usefulness for chronic therapy. Patients who do not respond to treatment with oral corticosteroids require hospitalization and intravenous steroids. Refractory symptoms may be treated with azathioprine or infliximab. Surgical treatment of ulcerative colitis is reserved for patients who fail medical therapy or who develop severe hemorrhage, perforation, or cancer. Longstanding ulcerative colitis is associated with an increased risk of colon cancer. Patients should receive an initial screening colonoscopy eight years after the onset of pancolitis and 12 to 15 years after the onset of left-sided disease; follow-up colonoscopy should be repeated every two to three years.