In 173 patients with surgically confirmed duodenal ulcer, malrotation of the duodenum (MD) was found in the pre-operative radiographs in a total of 54% without significant differences in the age and sex distribution. As compared with a control group, the frequency of MD was significantly increased in men and in patients over 50 years (Table I). The luminal diameter in the presence of MD was larger in the ulcer patients than in the control group (Table II). Gastric retention at 6 hours after the barium meal was more frequent in ulcer patients with MD than in those with normal duodenal configuration, and in both groups more frequent than in the control group. At a follow-up examination at least 12 months after the operation for duodenal ulcer, a significant tendency to a poorer result was revealed in patients with MD, manifested by persistent or postoperatively developed postcibal pain, fullness, nausea and vomiting (Table III-V), except in patients who had undergone parietal-cell vagotomy without pyloroplasty. The latter observation suggests that, in the presence of MD, preserved pyloric function is of significance in the frequency of subsequent manifest symptoms of this anomaly.