Aims/hypothesis Previous studies have suggested a possible connection between Helicobacter pylori (H. pylori) infection and diabetes risk. However, prospective studies examining direct associations between these two factors are relatively lacking. In this prospective cohort study, we aimed to evaluate the association between H. pylori infection and risk of developing diabetes. Methods We performed a population-based prospective study, recruiting participants aged 45-74 years and without diabetes from the Chinese Multi-provincial Cohort Study in 2002, with a 10 year follow-up to investigate development of diabetes. H. pylori serostatus was determined by measuring serum H. pylori antibodies. H. pylori seropositivity was defined as the antibody concentration >= 10 U/ml. To examine the association between H. pylori seropositivity and diabetes risk, modified Poisson regression was performed. Results Of 2085 participants without diabetes, 1208 (57.9%) were H. pylori seropositive in 2002. After multivariate adjustment of possible diabetes risk factors, H. pylori seropositivity was associated with lower risk of diabetes (RR 0.78 [95% CI 0.63, 0.97], p = 0.022). Of the 1275 participants with H. pylori antibody measurements in both 2002 and 2007, 677 (53.1%) were persistently seropositive. A lower risk of diabetes was also observed in participants with persistent H. pylori seropositivity (RR 0.61 [95% CI 0.41, 0.93], p = 0.020), compared with those persistently seronegative. Conclusions/interpretation H. pylori seropositivity was associated with lower risk of diabetes in this prospective cohort study. Extrapolation of these results and the mechanism underlying the observed association require further investigation.