During the period from August 1974 to December 1990, 115 cases of gastric, 97 of duodenal and 23 of combined gastroduodenal ulcer were operated on for gastroduodenal ulcer at the department. Among these cases, operation for perforation was carried out in 8 of gastric, 37 of duodenal and 3 of combined gastroduodenal ulcer. The incidences of perforation were 7.0%, 38.1% and 13.0%, respectively. Since all 3 cases of combined gastroduodenal ulcer developed perforation in the duodenal ulcer, these cases were included in the duodenal perforation group. The ratio of perforation in gastric to duodenal ulcer was 1:5, indicating that the majority of perforation occurred in the duodenal ulcer. The male to female ratio was 6:1, showing a high prevalence of males. Young men were more likely to have duodenal perforation than gastric perforation. The incidence of free air on the plain X-ray film was 75.0% in gastric perforation and 97.5% in duodenal ones. Epigastric sudden pain occurred in 50.5% of gastric and 87.5% of duodenal perforation cases, respectively. Anamnesis of ulcer disease was recognized in 62.5% of perforated gastric ulcer and 47.5% in perforated duodenal ulcer cases. The overall mortality rate was 8.3% (4 cases).