Most patients with symptomatic gallstones undergo cholecystectomy. Since smoking may influence gallstone formation by depressing postaglandin synthesis and mucus production in the gallbladder, we have examined smoking habits in a group of cholecystectomy patients. Two hundred and forty seven of 400 patients (62 %) responded to a comprehensive postal questionnaire with ‘buddy’ controls of the same age and sex. Patients and controls did not differ significantly in their age, weight, past medical history, drug usage or alcohol consumption. Female patients had had a mean of 2.4 (SD 1.8) pregnancies, female controls 2.0 (SD 1.5; p < 0.05, paired t test). Analysis of smoking habits in 178 female patients showed 32 % had smoked on average 18.4 cigarettes/day for a mean of 31 years whereas 52% of female controls had smoked 16.7 cigarettes/day for a mean of 37.0 years (p < 0.001, McNemar’s test for matched pairs). 39% of male patients smoked (21.7/day, 44.7 years) as compared to 61 % of male controls (23.1/day, 46 years; p < 0.01, McNemar’s test). The influence of number of cigarettes smoked, sex and weight were investigated by using a logistic regression. This showed evidence of a linear relationship between amount smoked and risk of gallstones (χ2 = 14.4, 1 d.f.p < 0.001). There was no evidence that the effect of smoking differed with age or weight. Symptomatic gallstones is predominantly a disease of non