In order to detect risk factors of gastric ulcer among male workers in Japan, a workplace-based case-control study was conducted in a municipal government, using cases registered during 1981 to 1983 with individually matched controls. Statistically significant factors in univariate analysis were smoking, time interval from waking up to leaving home for job, meal time for supper, sleeping hours, anxiety, and gloomy feeling. Logistic analysis showed that among the above factors the significant relative risks were 11.9 (95% confidence interval: 1.6-89.4) for 1-9 cigarettes per day, 9.9 (2.6-37.7) for 10 cigarettes or more per day, and 5.3 (1.6-17.5) for gloomy feeling. These findings obtained among the male Japanese workers were almost consistent with those epidemiologic results in other developed countries that smoking and personality traits are major risk factors of gastric ulcer.