The aim of this investigation was to clarify the histological characteristics of gastric cancer in the young. Twenty-three surgically resected specimens of young patients (under 30 years of age; young group) with intramucosal cancer of poorly differentiated type and 42 surgically resected specimens of elderly patients (more than 40 years of age; elderly group) with tumors of the identical depth and histological type were examined. The degree of gastritis and Helicobacter pylori (H. pylori) infection was evaluated according to the updated Sydney system. The incidence of H. pylori infection was significantly higher in the young group than in the elderly group (96 vs 36%, P<0.05). Within the background mucosa, antral chronic inflammatory infiltrates with lymphoid-follicle hyperplasia were more severe, and intestinal metaplasia was less frequent in the young group than in the elderly group. Glandular atrophy was not different between the two groups. Intramucosal gastric adenocarcinomas of poorly differentiated type in the young may be associated with H. pylori infection with antral chronic inflammation with lymphoid-follicle hyperplasia, regardless of the existence of intestinal metaplasia within the background gastric mucosa.