The present study is an attempt to assess the risks of the complications associated with recurrent ulcers in patients who have undergone gastric surgery and to determine whether these risks differ from those observed in patients receiving long term maintenance treatment with H2-receptor antagonists for ulcer disease. One hundred and thirty studies reported in the literature during the past three decades have been analysed to determine both the approximate rate of ulcer recurrence and the proportion of patients with recurrent ulcers who have presented with either haemorrhage or perforation following the various types of gastric surgery for ulcer disease. From these data, estimates of the risks of haemorrhage and of perforation during the years following gastric surgery have been calculated. Vagotomy and antrectomy is associated with a low risk of ulcer recurrence (less than 1%) and the risk of complications in later years is accordingly very small (less than 0.5%). Partial gastrectomy, although associated with low recurrence rates, has a higher risk of complications (1.3% for haemorrhage, 0.3% for perforation) because the proportion of recurrent ulcers that present with haemorrhage or perforation is high (33% and 8%, respectively). Truncal vagotomy plus drainage (TV + D) and highly selective vagotomy (HSV) are associated with recurrence rates of 9% and 12%, respectively, but ulcer recurrences following these operations are less frequently accompanied by complications then recurrences after gastric resection and, as a result, the risks of haemorrhage (1.7% for TV + D; 1.3% for HSV) are similar to the risks after gastric resection. During long term (five years or more) maintenance treatment with H2-receptor antagonists, the risks of haemorrhage and perforation are less than 2% and less than 0.5%, respectively. It appears, therefore, that the likelihood of developing haemorrhage or perforation following gastric surgery is of the same order as that during maintenance treatment with H2-receptor antagonists, at least during the first decade of follow-up.