Because the efficacy of UDCA on long-term outcome of primary biliary cirrhosis (PBC) has not been completely elucidated, we have assessed the course and survival of patients with PBC treated with UDCA and compared with the survival predicted by the Mayo model and the estimated survival of a standardized population. (One hundred ninety-two patients [181 women] with PBC treated with UDCA [15 mg/kg per day] for 1.5-14 years.) Response to treatment was defined by an alkaline phosphatase decrease greater than 40% of baseline values or normal levels after 1 year of treatment. The predicted survival was obtained by the Mayo model and the estimated survival was taken from the standardized matched Spanish population. Seventeen patients died or fulfilled criteria for liver transplantation (8.9%). The observed survival was higher than that predicted by the Mayo model and lower than that of the control population (P < .001). One hundred seventeen patients (61%) responded to treatment. The survival of responders was significantly higher than that predicted by the Mayo model and similar to that estimated for the control population (P = .15). By contrast, the survival of patients without biochemical response was lower than that estimated for the Spanish population (P < .001) although higher than that predicted by the Mayo model. Biochemical response to UDCA after 1 year is associated with a similar survival to the matched control population, clearly supporting the favorable effects of this treatment in PBC. The suboptimal survival of nonresponders identifies the group for further treatments.