All patients greater than or equal to 16 years old with a diagnosis of ulcerative colitis were identified in five well-defined catchment areas, representing 12.7% of the Swedish population. Exactly 1500 patients were retrieved, giving a point prevalence of 170/10(5) inhabitants. It was possible to obtain liver function test results less than 2 years old in 94% of the patients and to obtain endoscopic retrograde cholangiographic results in 65 of the 72 patients with abnormal serum alkaline phosphatase values. Primary sclerosing cholangitis was diagnosed in 55 of the patients (3.7%). The prevalence of the disease was 5.5% in patients with substantial colitis and 0.5% in patients with distal colitis. There was a marked male predominance in cholangitis patients compared with colitis patients without cholangitis. Ninety-five percent of the patients with cholangitis had substantial colitis, which was more than the 62% of patients without cholangitis who had colitis. Female patients with cholangitis were older than male patients at the time of diagnosis of both cholangitis and colitis, which contrasted to the equal age at diagnosis of colitis in male and female patients without cholangitis.