AIM: To describe the frequency of H pylori infection among 1000 southern Iranian dyspeptic patients. METHODS: A prospective study was performed in a referral hospital in south of Iran from 1999 to 2005. One thousand dyspeptic patients (518 males, mean ± SD age of 49.12 ± 12.82 years) consecutively underwent upper gastrointestinal endoscopy. Multiple gastric antral biopsy samples were taken from all patients for rapid urease test and histopathologic examination (96.9% satisfactory samples). Patients were considered H pylori-infected if one or both tests were positive. RESULTS: Six hundred and seventy-one patients (67.1%, 95% confidence interval [CI]: 64.2%-70.0%) were H pylori-infected. H pylori positivity was significantly more frequent in patients with peptic ulcer disease (PUD) than in those with non-ulcer dyspepsia (P < 0.001). Male-to-female ratio for duodenal and gastric ulcers was 2.7:1 and 1.5:1, respectively. Moreover, the duodenal- to-gastric ulcer ratio was 1.95:1. The frequency of H pylori infection among those with endoscopic diagnosis of gastritis, duodenal ulcer, gastric ulcer, and normal mucosa was 70.1% (398/568), 86.2% (150/174), 71.9% (64/89), and 33.5% (54/161), respectively. H pylori infection, male sex, and older age were independently associated with PUD in multivariate analysis. H pylori positivity was associated with chronic gastritis, and chronic active gastritis with odds ratios of 34.21 (95% CI: 12.19%-96.03%) and 81.21 (95% CI: 28.85%-228.55%), respectively. CONCLUSION: H pylori and PUD are highly frequent in dyspeptic patients from south of Iran. H pylori is a cardinal risk factor for chronic active or inactive gastritis. AIM: To describe the frequency of H pylori infection among 1000 southern Iranian dyspeptic patients. METHODS: A prospective study was performed in a referral hospital in south of Iran from 1999 to 2005. One thousand dyspeptic patients (518 males, mean ± SD age of 49.12 ± 12.82 years) consecutively underwent upper gastrointestinal endoscopy. Multiple gastric antral biopsy samples were taken from all patients for rapid urease test and histopathologic examination (96.9% satisfactory samples). Patients were considered H pylori-infected if one or both tests were positive. RESULTS: Six hundred and seventy-one patients (67.1%, 95% confidence interval [CI]: 64.2% -70.0%) were H pylori-infected. H pylori positivity was significantly more frequent in patients with peptic ulcer disease Male-to-female ratio for duodenal and gastric ulcers was 2.7: 1 and 1.5: 1, respectively. Moreover, the duodenal-to-gastric ulcer ratio was 1.95: 1 in those with non-ulcer dyspepsia (P <0.001) The freq uency of H pylori infection among those with endoscopic diagnosis of gastritis, duodenal ulcer, gastric ulcer, and normal mucosa was 70.1% (398/568), 86.2% (150/174), 71.9% (64/89) (54/161), respectively. H pylori infection, male sex, and older age were independently associated with PUD in multivariate analysis. H pylori positivity was associated with chronic gastritis, and chronic active gastritis with odds ratios of 34.21 (95% CI: CONCLUSION: H pylori and PUD are highly frequent in dyspeptic patients from south of Iran. H pylori is a cardinal risk factor for chronic active or inactive gastritis.