Primary biliary cirrhosis (PBC) is a disease of unknown etiology, with unexplained geographical variation. Various exposures have been suggested as triggers for disease development-possibly in susceptible individuals, but the evidence was not always well founded. We therefore conducted a population-based case-control study in Northeast England to investigate these and other exposures. All cases incident during 1993 to 1995 in a defined area of Northeast England were identified, and age- and sex-matched population controls were identified from primary care population registers. Cases and controls were sent postal self-completion questionnaires covering medical history and lifestyle. Information was received from 100 cases and 223 controls. The familial tendency of PBC was found to be less marked than has been claimed: Only weak associations were found with other autoimmune diseases. Among factors considered previously, no significant associations were found with surgical procedures, events in pregnancy, past infections, vaccinations, and medications. No significant associations were found for previously unconsidered lifestyle factors (drinking alcohol, previous pets, or stressful events), but there was an unexpected association with past smoking (ever smoked: 76% in cases vs. 57% in controls, odds ratio 2.4; smoked for 20 years or more: 64% vs. 35%, odds ratio 3.5). There were also unexpected significant associations with psoriasis (13% in cases vs. 3% in controls, odds ratio 4.6) and eczema (3% in cases vs. 11% in controls, odds ratio 0. 13). These findings merit further investigation.