The relationship between the risk of biliary tract cancers and menstrual and reproductive factors has been studied in a case-control study conducted in Milan, northern Italy, between January 1984 and February 1993 on 31 incident, histologically confirmed cases and 377 controls in hospital for acute, non-neoplastic, non-gynaecological, non-hormone-related conditions. Odds ratios (ORs) together with their corresponding 95% confidence intervals (CIs) and the significance of the linear trends in risk were estimated by unconditional multiple logistic regression, after adjustment for age and cholelithiasis. Menopause was associated with a decreased risk of biliary tract cancers (OR 0.2), while late menopause and the use of hormone replacement therapy tended to increase the risk (ORs 1.8 and 2.2 respectively). Age at menarche and regular menstrual cycles were not associated. A trend in risk was found with parity, while total abortions and age at first and last birth were not related. Thus, the protective effect of early menopause and the apparent association of multiple full-term pregnancies suggest a role of female hormones in the aetiology of biliary tract cancers.