BACKGROUND/AIMS--The course of primary sclerosing cholangitis (PSC) is highly variable and unpredictable. This study describes the natural history and outcome of PSC. These data were used to construct a prognostic model for patients with PSC. METHODS--A total of 305 Swedish patients with PSC were studied. The median follow up time was 63 (1-194) months and all patients could be traced for follow up. Some 79 patients died or had a liver transplant. The prognostic significance of clinical, biochemical, and histological findings at the time of diagnosis were evaluated using multivariate analysis. RESULTS--The estimated median survival from time of diagnosis to death or liver transplantation was 12 years. Cholangiocarcinoma was found in 24 (8%) of the patients and 134 (44%) of the patients were asymptomatic at the time of diagnosis. The estimated survival rate was significantly higher in the asymptomatic group (p < 0.001). However, 29 (22%) of the asymptomatic patients became symptomatic during the study period. It was found that age, serum bilirubin concentration, and histological stage at the time of diagnosis were independent predictors of a bad prognosis. These variables were used to construct a prognostic model. CONCLUSIONS--This prognostic model developed from a large homogeneous population of PSC patients should be of value for the timing of transplantation and patient counselling in PSC.