OBJECTIVE To evaluate the prevalence of (Hp) infection in a group of inflammatory bowel disease (IBD) outpatients and the possible influence of treatment. BACKGROUND The low prevalence of Hp infection in these patients is usually attributed to environmental factors; the role of drugs has not been fully investigated. METHODS Seventy-two consecutive outpatients underwent a C13-urea breath test for Hp: 32 with Crohn's disease (13 men; mean age, 48 years; range, 20-72 years) and 40 with ulcerative colitis (25 men; mean age, 49 years; range, 25-71 years). Thirty-one patients were treated with sulfasalazine and 41 with 5-ASA. The control group consisted of 72 age- and sex-matched subjects. RESULTS The prevalence of Hp infection was 47% in the IBD patients and 61% in the controls (p = 0.089; odds ratio = 0.55; 95% CI = 0.283-1.089) with a statistically significant increase for each year of age ( p= 0.044; odds ratio = 1.02; 95% CI = 1.001-1.052). Among the IBD patients, age and gender, the type, activity, duration, extent of the disease, or the calendar year of diagnosis, had no influence on Hp infection. was detected in 65% of the patients treated with sulfasalazine and in 34% treated with 5-ASA (p = 0.017). CONCLUSIONS Although low, the prevalence of Hp infection in our patients was not significantly different from that in the controls. 5-ASA, and not sulfasalazine, may have a protective effect against Hp infection.