Maastricht University, Department of Epidemiology, The Netherlands. STUDY OBJECTIVE: To study the association between socioeconomic status (SES) and stomach cancer incidence (cardia and non-cardia) and the role of lifestyle factors in explaining this association. DESIGN: Prospective cohort study on diet and cancer that started in 1986. Data were collected by means of a self administered questionnaire. SETTING: Population originating from 204 municipalities in the Netherlands. PARTICIPANTS: 58,279 men aged 55-69 years. After 4.3 years of follow up, 162 incident stomach cancer cases were detected (49 cardia and 113 non-cardia cases). MAIN RESULTS AND CONCLUSIONS: After adjustment for age, a lower overall stomach cancer risk was found for men with the highest attained level of education (RR highest/lowest level = 0.54, 95% CI 0.33, 0.89, trend, p = 0.02). This association became less strong after additional adjustment for smoking, intake of vitamin C, beta carotene, alcohol and coffee, family history of stomach cancer, and history of stomach disorders (RR = 0.61, 95% CI 0.34, 1.07, trend, p = 0.11). No clear association was found between occupation based SES indicators and stomach cancer risk. Analyses per subsite of stomach cancer revealed that for people with the highest level of education the age adjusted rate ratio for cardia cancer changed from 0.37 (95% CI = 0.13, 1.00) to 0.60 (95% CI = 0.19, 1.87) after additional adjustment for lifestyle variables, whereas the rate ratio for non-cardia cancer (RR = 0.59, 95% CI 0.33, 1.05) did not change after additional adjustment.