To assess primary antibiotic resistance in a given population and relate the results to ethnicity. Consecutive cultures were tested for antibiotic susceptibility with the Etest. Three populations were studied separately: ethnic Dutch people, patients of Turkish descent, and patients originating from Africa and the Middle East. Over a period of 5.5 years, 976 (32%) biopsy specimens from 3010 patients were positive for Helicobacter pylori. Metronidazole and clarithromycin resistance were present in 25.8% and 4.8% of the strains, respectively. The number of metronidazole-resistant strains showed a gradual decrease, while clarithromycin resistance showed a slight increase during the study period. Antimicrobial resistance in patients of Turkish descent and in those originating from Africa or the Middle East was significantly higher than in ethnic Dutch people, 35% and 9.1% versus 21% and 2.9%, respectively (P = 0.003 and P = 0.002). It is important to take ethnicity into account when studying antibiotic resistance. The numbers of metronidazole- and clarithromycin-resistant strains can vary considerably between people of different ethnic origin living in the same region.