Background: Prevalence of peptic ulcer disease has been associated to diet. Some dietary factors seem to have bactericidal effect which may modify the risk of peptic ulcer disease. The objective was to analyze associations between dietary habits and peptic ulcers. Design: A cross sectional population study. Subjects: One thousand, one hundred and thirty-®ve subjects out of 11 700 randomly invited men and women, aged 46±67 y, participating in a diet and disease study during 1991±1993. The study population comprised of 764 cases with reported peptic ulcer, 142 with dyspeptic symptoms and 229 randomly selected controls. Methods: X-ray examinations and endoscopies were reviewed and 332 out of 764 peptic ulcer cases were veri®ed. Mean daily intake of foods and nutrients were assessed with a combined 7 d menu book and a quantitative food frequency questionnaire, including dietary supplements. Results: Subjects with veri®ed ulcer had lower intake of fermented milk products and vegetables and higher intake of milk, meat and bread than controls. Intake of total fat, saturated and monounsaturated fatty acids and linolenic acid were higher in the ulcer group. Higher intake of fermented milk products, by quintiles showed a decreased ulcer risk; odds ratio 0.82 (0.71±0.95), adjusted for covariates below. Higher intake of milk, by quintiles, was associated with an increased risk of ulcer; odds ratio 1.17 (1.03±1.32). Smoking, foreign ethnicity and being unmarried or divorced were covariates associated to ulcer. Conclusion: This study indicates the multifactorial etiology of peptic ulcer including dietary factors. High intake of fermented milk products was associated with decreased risk for ulcer, whereas increased risk was noted for high milk intake. Sponsorship: The study was supported by the Swedish Cancer Society.