The incidence and prevalence of gallstones has been documented in 289 consecutive patients with peptic ulcer disease, at the time of antrectomy and gastroduodenostomy (with or without truncal or selective vagotomy) and again during a 5-year follow-up period. By comparing the preoperative prevalence of gallstone disease in one age group with the prevalence 5 years after the gastric operation in another group of patients who were 5 years younger at the operation, the incidence of gallstone production due to the gastric operation could be calculated independent of the age factor. Within 5 years of the gastric operation, 18% of the patients who were normal at the time of operation produced gallstones. The incidence of new gallstones during the 5-year postgastrectomy follow-up was the same in men and women, and was increased by 7 to 15% in each age group of men. The incidence of new gallstones was 30% after truncal and 12% after selective vagotomy (p less than 0.05). Gallstone formation seems to be a sequel of Billroth I gastric resection. Truncal vagotomy in addition to the gastrectomy increases the risk of gallstone disease; patients with selective vagotomy and antrectomy had an incidence of postoperative gallstones which was the same as patients with antrectomy alone.