Background: Helicobacter pylori antimicrobial resistance is the most common reason for eradication failure. Small studies have shown metronidazole resistance to be more prevalent in certain population groups. Aim: To determine the resistance rates in a large cohort of patients from a single centre in the UK, and to evaluate resistance patterns over time, according to age, sex and socio-economic status. Methods: Consecutive patients with H. pylori-positive antral gastric biopsy samples were studied from 1994 to 1999, Susceptibility testing was performed to metronidazole, tetracycline, macrolide and amoxicillin by the modified disk diffusion method. The Jarman under-privileged area score was used as a measure of socioeconomic status. Results: A total of 1064 patients were studied. Overall metronidazole resistance was 40.3%, decreasing with age (P < 0.0001, odds ratio for patients over 60 years 0.63, 95% CI: 0.48-0.80). Women were more likely to have metronidazole resistant strains (P = 0.003, odds ratio 1.5, 95% Cl: 1.15-1.91), but there was no association with Jarman score. Macrolide resistance was associated with metronidazole resistance (P = 0.03, odds ratio 2.14, 95% Ch 1.07-4.28). Conclusions: Metronidazole resistance in H. pylori is highly prevalent and more common in women and the young, but does not appear to be related to socioeconomic status.