OBJECTIVES: To identify risk factors of carcinoma of the extrahepatic biliary tract in men. METHODS: Newly diagnosed and histologically confirmed patients, 35-70 years old, were interviewed between 1995 and 1997 in Denmark, Sweden, France, Germany and Italy. Population controls were frequency-matched by age and region. Adjusted odds ratios and 95%-confidence intervals were estimated by logistic regression. RESULTS: The analysis included 153 patients and 1421 controls. The participation proportion was 71% for patients and 61% for controls. Gallstone disease was corroborated as a risk factor for extrahepatic biliary tract carcinoma in men (odds ratio 2.49; 95% confidence interval 1.32-4.70), particularly for gall bladder tumors (odds ratio 4.68; 95% confidence interval 1.85-11.84). For a body mass index [height (m) divided by squared weight (kg2)] >30 at age 35 years, an excess risk was observed (odds ratio 2.58; 95% confidence interval 1.07-6.23, reference: body mass index 18.5-25) that was even stronger if the body mass index was >30 for the lowest weight in adulthood (odds ratio 4.68; 95% confidence interval 1.13-19.40). Infection of the gall bladder, chronic inflammatory bowel disease, hepatitis or smoking showed no clear association, whereas some increase in risk was suggested for consumption of 40-80 g alcohol per day and more. CONCLUSIONS: Our study corroborates gallstones as a risk indicator in extrahepatic biliary tract carcinoma. Permanent overweight and obesity in adult life was identified as a strong risk factor for extrahepatic biliary tract carcinoma, whereas we did not find any strong lifestyle-associated risk factors. Inconsistent results across studies concerning the association of extrahepatic biliary tract carcinoma with overweight and obesity may be explained by the different approaches to assess this variable.