84 patients underwent multiple abdominal ultrasound examinations over a median of 36 months (range 6-140). 11 had gallstones at their first ultrasound examination, and were excluded from further analysis. Of the remaining 73 patients, 12 of 47 who underwent major abdominal surgery had gallstones within 14-36 months of operation, compared with 0 of 26 who did not undergo such surgery. The cumulative prevalence of new gallstones within 3 years of major surgery was 28%; no new gallstones were seen from 36 to up to 140 months postoperatively. By univariate and logistic regression analysis, age and major abdominal surgery were the only significant clinical determinants for the appearance of gallstones during follow-up. The findings of this retrospective study indicate that major abdominal surgery may accelerate the development of gallstones in some patients. If confirmed in a prospective study, it may be possible to define groups at high risk of gallstones after surgery and to institute prophylactic measures.