Colonization of the human stomach with Helicobacter pylori induces chronic gastritis and is associated with the development of gastric and duodenal ulcers, gastric carcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Infection with an H. pylori strain containing the cytotoxin-associated (cagA) gene (a marker for a pathogenicity island) may increase the risk of atrophic gastritis and gastric cancer. The exact role of H. pylori in gastric carcinogenesis is still being investigated. Hence, we assessed whether H. pylori infection is associated with the development of gastric adenocarcinoma in northern Iran. Gastric biopsy specimens from 168 patients suffering from gastric adenocarcinoma, gastric ulcer, and non-ulcer dyspepsia were analyzed by means of the polymerase chain reaction. H. pylori was detected in the gastric mucosa of 34 (75.5%) gastric adenocarcinoma, 56 (88.8%) gastric ulcer, and 36 (60%) non-ulcer dyspepsia. In patients with gastric adenocarcinoma, the cagA was less commonly found than those in noncancer patients (4/34 vs. 58/92, p < 0.05). Our work suggests that although H. pylori infection is significantly associated with gastric adenocarcinoma in northern Iran, the cagA is not the dominant virulence in development of gastric adenocarcinoma.