Twenty patients without symptoms of hepatobiliary disease were diagnosed as having asymptomatic primary biliary cirrhosis. In every patient liver histology was diagnostic of, suggestive of, or compatible with the diagnosis. Eighteen had a positive serum mitochondrial antibody, 18 had raised serum immunoglobulin M, and 17 had markedly raised serum alkaline phosphatase values. A mean of 4.5 years after diagnosis, 10 of the patients had not developed hepatobiliary symtoms; 4 of these 10 patients have survived 6 to 10 years. Ten patients developed symptoms after a mean of 2.2 years from initial diagnosis; 7 are still alive but 3 have died of liver failure. The development of symptoms could not be predicted by either serum biochemical tests or hepatic histology. It is concluded that the diagnosis of asymptomatic primary biliary cirrhosis is compatible with 10 or more asymptomatic years.