To identify the high-risk group having a large number of cancerous lesions in the stomach, the histopathological characteristics of multifocal gastric cancer in 38 young patients (49 years old or younger, group A) were studied and compared with 204 older patients (at least 50 years old, group B). In terms of the number of foci, patients with over 4 foci (high-risk patients) were more frequent in group A (20%) than in group B (5%, p < 0.05). In 80% of the patients in group A, each focus was near the borderline of both glands (pyloric and fundic glands) and was not always surrounded by intestinal metaplasia, while in 70% of the group B patients the lesions were scattered throughout the stomach and were surrounded by intestinal metaplasia. The carcinogenesis of multifocal cancer in group A, which differs from that in group B, might be stimulated by some strong carcinogenic promoters.