Background: Marked differences in prevalence of Helicobacter pylori have been noted between population subgroups living in the same country. A cross-sectional endoscopical study in consecutive patients presenting with active ulcer disease was done., in order to study the H. pylori prevalence in relation to ethnicity in ulcer patients. Methods: Consecutive patients with an active duodenal or gastric ulcer were eligible for inclusion. Biopsy specimens from the gastric antrum were taken for detection of H. pylori, People originating from Turkey were studied separately. Results: In an 8-year period, 375 patients with active duodenal ulcer were seen. Three hundred one patients were ethnic Dutch. Seventy-four of the patients were of Turkish origin. These were statistically significant younger than ethnic Dutchmen, 35.9 vs. 61.2 years (P < 0.0001). The number of men was significantly higher, 82.4% vs. 53.8% (P < 0.001). H. pylori prevalence was significantly higher in Turkish patients with duodenal ulcer, 91 vs. 74% (P < 0.0001). Gastric ulcer was seen in 218 patients. Only five patients were of Turkish descent. The number of Turkish patients was too small to permit statistical analysis, but the percentage of men is higher and the mean age is lower compared with ethnic Dutchmen. Conclusions: It is concluded that if ulcer disease and H. pylori prevalence is studied in a given population, ethnicity of the population understudy has to be taken into account. (C) 2001 Elsevier Science B.V. All rights reserved.