The prevalence of gallstone disease and associated factors in the entire population of subjects aged 15-65 years born and resident in Chianciano Terme (Siena - Tuscany) was examined in the years 1985 and 1986. The investigation included gallbladder ultrasonography, administration of a questionnaire on personal and family history, physical examination and blood chemistry. A total of 1809 subjects (attendance rate 87.7%) participated in the study. Personal history and physical examination showed that Chianciano inhabitants have a low prevalence of obesity (4.3%) and only 4.4% of the female population had more than two pregnancies. Overall prevalence of gallstone disease (cholecystectomy+cholelithiasis) was 5.9% (3.7% for males and 8.4% for females). Age standardized relative risk of gallstone disease for females was 2.25 (95% confidence limits = 1.68-2.68). Prevalence of cholelithiasis was 3.5% (2.7% for males and 4.2% for females). Prevalence of gallstone disease increased with increasing age in both sexes, being extremely low in the age interval of 15-29 years (0.25%). The overall gallstones/cholecystectomy ratio was found to be lower (1:1) in females than in males (2.7:1). Although subjects with gallstones reported more frequently biliary colics and non-specific dyspeptic symptoms, the diagnostic power of all symptoms in identifying cholelithiasis was very poor due to low sensitivity. Only one third of subjects with gallstones was aware of having the disease. Age, obesity and number of pregnancies were positively associated with gallstone disease in univariate analyses. The association with obesity and parity disappeared in multivariate analysis. Blood lipids and glucose were not associated with the disease both in univariate and multivariate analyses.(ABSTRACT TRUNCATED AT 250 WORDS)