A comparative case-referent study was conducted using data from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), with the aim of clarifying whether histologic subtypes of gastric cancer exhibit different risk-factor patterns of habitual smoking. Our study comprised 995 histologically confirmed gastric-cancer cases [460 differentiated (intestinal type), 527 non-differentiated (diffuse type) and 8 unclassified], identified via hospital cancer registry and surgical records, and 43,846 non-cancer outpatients at Aichi Cancer Center Hospital over the years 1988-1995. Odds ratios (ORs) were estimated by gender using logistic regression and adjusted for potential confounding factors. In males, a significantly increased OR of gastric cancer was observed for habitual smokers, and this was higher in the differentiated type than the non-differentiated type and in younger than in older age groups. Risk patterns were less clear in females. Our results suggest that habitual smoking is associated more likely with the differentiated type of gastric cancer, particularly in younger cases.