Although the etiology of primary biliary cirrhosis (PBC) remains unknown, environmental factors may act to trigger the disease in genetically susceptible hosts. To assess specific risk factors, we conducted a survey using standardized NHANES questions to 241 PBC patients in the United States, 261 of their siblings, and 141 friends without PBC. The overall response rate was 199 of 241 (83%) among PBC cases, 171 of 261 (67%) among siblings, and 141 of 225 (62. 7%) among friend controls. The female-to-male ratio among cases in this sample was approximately 10:1; the mean age was 53 years, and 97% were Caucasian. Other autoimmune diseases reported most frequently by PBC cases included Sjogren's syndrome (17.4%) and Raynaud's syndrome (12.5%). Approximately 6% of cases reported at least one family member with PBC. Adjusted odds ratios (OR) were elevated for cases compared with friends for other autoimmune diseases (OR = 4.92, 95% confidence interval [CI] = 2.38, 10.18), smoking (OR = 2.04, 95% CI = 1.10, 3.78), tonsillectomy (OR = 1.86, 95% CI = 1.02, 3.39), and vaginal or urinary tract infection (UTI) in females only (OR = 2.12, 95% CI = 1.10, 4.07). Similarly elevated ORs were observed for these risk factors when cases were compared with their siblings. The higher rate of UTI among cases is particularly interesting in light of previous data, and raises the possibility of an infectious etiology for PBC and of molecular mimicry as an etiologic mechanism. The significance of smoking in the multivariate models supports the findings of previous studies and raises the issue of the influence of smoking on a Th1 response.