In 2003, a 69-year-old man visited our emergency department because of hematemesis and anemia. Emergency gastroscopy revealed massive bleeding from Dieulafoy's ulcer in the upper body of the stomach. The arterial bleeding was successfully controlled by endoscopic clipping. Blood transfusion and a proton-pump inhibitor were administered and his condition recovered smoothly. Two weeks after the treatment, type IIa early gastric cancer was detected at the previous bleeding point by follow-up endoscopy. He underwent distal gastrectomy with systematic lymph node dissection (D2), and he had no sign of recurrence until 2005. Histopathological examination revealed an early gastric cancer with submucosal invasion located just above the Dieulafoy's disease. The characteristic finding of Dieulafoy's disease was an enlarged and tortuous artery arising from the subserosa, penetrating the muscle layer, and spreading in the submucosa. Abnormal Dieulafoy's artery coexisting with gastric cancer has been reported in only 17 cases until now. Our clinical and pathological findings led us to the following speculation on the pathogenesis in our patient. Repeated regeneration of the mucosal membrane would have been caused by circulatory disturbance in Dieulafoy's vessels. This regeneration and mucosal dysplasia may have been a factor in promoting the gastric cancer. In the previously reported cases of the coexistence of abnormal Dieulafoy's artery and gastric cancer, the initial gastroscopic examination rarely diagnosed the gastric cancer. Thus, follow-up gastroscopy is essential, so as not to miss such coexisting diseases.