BACKGROUND Helicobacter pylori infection is associated with gastric cancer, but the effect of eradication treatment on gastric cancer risk is not well defined. OBJECTIVE To determine whether H. pylori eradication treatment can reduce the risk for gastric cancer. METHODS PubMed, EMBASE, Cochrane Library, Google Scholar, and online clinical trial registers through 31 January 2009, without language restrictions. METHODS Randomized trials that compared eradication treatment with no treatment in H. pylori-positive patients and that assessed gastric cancer or progression of preneoplastic lesions during follow-up. METHODS Two authors independently reviewed articles and extracted data. RESULTS Seven studies met inclusion criteria, 1 of which was excluded from pooled analysis because of clinical and methodological heterogeneity. All studies were performed in areas with high incidence of gastric cancer, mostly in Asia. Overall, 37 of 3388 (1.1%) treated patients developed gastric cancer compared with 56 of 3307 (1.7%) untreated (control) participants. In a pooled analysis of 6 studies with a total of 6695 participants followed from 4 to 10 years, the relative risk for gastric cancer was 0.65 (95% CI, 0.43 to 0.98). CONCLUSIONS All studies but 1 were performed in Asia. Only 2 assessed gastric cancer incidence, and only 2 were double-blinded. CONCLUSIONS Helicobacter pylori eradication treatment seems to reduce gastric cancer risk.