Background & Aims Although eradication of Helicobacter pylori infection reduces the risk of gastric cancer, few data are available on its effects in older subjects. We compared the age-specific risk of gastric cancer in a large cohort of subjects who received H pylori eradication therapy vs a matched general population. Methods We searched the Hospital Authority database of Hong Kong to identify individuals with H pylori infection who had received a course of clarithromycin-containing eradication therapy from January 2003 through December 2012. We compared the gastric cancer incidence in this cohort with the expected incidence for the local general population by retrieving the gastric cancer incidence of the age- and sex-matched population from 2003 through 2014 (the latest available year) from the Hong Kong Cancer Registry. The primary outcome was the incidence of gastric cancer development in the cohort treated for H pylori infection vs the expected number of gastric cancer cases in the general population. Analyses were conducted by a priori age groups of less than 40 years, 40–59 years, and 60 years or older. Results Among 73,237 subjects infected with H pylori who received eradication therapy, 200 (0.27%) developed gastric cancer during a median follow-up time of 7.6 years. Compared with the matched general population, the gastric cancer risk was significantly lower in subjects 60 years or older who had received H pylori treatment (standardized incidence ratio [SIR], 0.82; 95% confidence interval [CI], 0.69–0.97; P = .02) but not in younger groups. When data were stratified based on time from H pylori treatment (less than 5 years, 5–9 years, and 10 or more years), the risk of gastric cancer was significantly lower than the general population 10 or more years after eradication in the group 40–59 years old (SIR 0.32; 95% CI, 0.08–0.88; P = .04) and the group 60 years or older (SIR, 0.42; 95% CI, 0.42–0.84; P = .02) than the other age groups. Conclusions In an analysis of data from a public hospital datab...