['The significance of diabetes mellitus (DM) in gastric carcinogenesis still remains unclear. We investigated whether DM would be a risk factor for the development of early gastric cancer.', 'Factors related to the presence of gastric cancer were examined in patients undergoing medical health checkups. We then investigated whether DM was related to the development of early gastric cancer during an endoscopic follow-up study.', 'Gastric cancer was detected in 14 (1.0%) of 1463 patients at the first endoscopic examination and was significantly associated with the severity of gastric atrophy and the presence of DM. During the follow-up period (range 36-108 months; mean 70.0 months), early gastric cancer was newly detected in 26 (1.8%) of the 1449 patients in whom gastric cancer had not been detected at the first examination. Gastric cancer was detected in 17 (1.3%) of 1301 patients without DM, and in 9 (6.1%) of 148 patients with DM (P < 0.0001). Multivariate analyses demonstrated that open-type gastric atrophy and DM were independently related to the development of early gastric cancer (P < 0.0001 and P = 0.020, respectively). Gastric cancer was identified in 14 (5.1%) of 274 patients who had open-type atrophic gastritis without DM, whereas it was identified in 8 (16.0%) of 50 patients who had both open-type atrophic gastritis and DM (P = 0.0042).'] Does diabetes mellitus increase the risk of early gastric cancer development?