A case control study of gastric cancer in coal miners was conducted. Forty six cases of gastric cancer and 138 comparisons drawn from four NIOSH coal miner cohorts were used. Three series of age matched miners were developed for each gastric cancer case: miners who died from lung cancer, miners who died from cancer other than gastric or lung cancer, and miners who died from noncancer, nonaccident causes. Odds ratios (ORs) were used as a measure of the relative risk of gastric cancer. ORs for gastric cancer were computed as a function of years of exposure to coal mine dust, cigarette smoking, or history of coal workers' pneumoconiosis. Coal mine dust exposure itself was a slightly elevated gastric cancer risk. When the coal mine dust exposure risk was examined under control by cigarette smoking status, the risk was statistically increased in miners with prolonged exposure to cigarette smoke. Coal workers' pneumoconiosis was not found to be a gastric cancer risk. The author concludes that among United States coal miners, an occupational gastric cancer risk due to exposure to coal mine dust exists, but only when a life style feature, cigarette smoking, is also present. When prolonged coal mine dust exposure in conjunction with prolonged cigarette smoking occurs, the risk of gastric cancer is statistically significant.