BACKGROUND/AIMS: The aim of the present study was to investigate the familial occurrence of autoimmune diseases in a large group of patients with primary sclerosing cholangitis (PSC). METHODS: All patients with PSC treated at Huddinge University Hospital between 1984 and 1999 were included (n=145). For every patient with PSC and inflammatory bowel disease (IBD) (n=126) we randomly selected a control patient with IBD (n=126), matched for age, sex and type of IBD. A questionnaire comprising information about autoimmune diseases among first-degree relatives was answered by all patients and controls. RESULTS: We identified 22 index cases with PSC from 21 families with a first-degree relative with either chronic liver disease and/or IBD. Five patients with PSC had a first-degree relative with PSC (3.4%). The prevalence of PSC among first-degree relatives was 0.7% (5/717). In siblings the prevalence was 1.5% (4/269). The prevalence of first-degree relatives with autoimmune diseases outside the liver was similar in PSC patients and controls. CONCLUSIONS: First-degree relatives of patients with PSC have a PSC prevalence of 0.7%. This represents a nearly 100-fold increased risk of developing PSC compared with the general population, supporting the hypothesis that genetic factors are of importance for development of PSC.