AbstractFactors thought to be important in the development of recurrent ulcer after proximal gastric vagotomy were investigated 1–4 years after operation in 211 patients with duodenal ulcer and in 49 with pre‐pyloric ulcer. Recurrent ulcer was found in 25 patients with duodenal ulcer (12 per cent) and in 6 with pre‐pyloric ulcer (12 per cent). Recurrence was not related to age, sex, duration of dyspepsia, radiological findings or peak acid output before and 10 days after vagotomy. Fiftysix patients were operated upon by the method of Amdrup and Jensen (1970), including skeletonization of about 2 cm of the oesophagus. The remaining 204 patients were operated on by a technique in which the dissection of the lesser curve was begun at the ‘crow's foot’ and the oesophageal dissection was extended, in most cases, to more than 4 cm above the cardia. Recurrence was more frequent among the 56 patients in the first group than among the remaining patients with duodenal ulcer. Recurrence was positively related to basal acid output after vagotomy. An increase of peak acid output of 50 per cent was seen in a smaller group with recurrence and patients with dyspepsia within 18 months of vagotomy.It was concluded that the risk of recurrence is not related to the number of parietal cells, as expressed by peak acid output to histamine. The risk may probably be reduced by extension of the oesophageal skeletonization. A marked increase in peak acid output may be seen during the first year after proximal gastric vagotomy in patients with recurrence or