Although the incidence of gastric carcinoma in Japan has declined in the past several decades, there is no information about trends in helicobacter pylori infection. The purpose of the study was to clarify trends in H. pylori infection and in histologic gastritis in young Japanese subjects evaluated between 1975 and 1978 (the 1970s) versus 1991 and 1994 (the 1990s). The prevalence of H. pylori infection and the grade of gastritis in biopsy specimens were evaluated in 173 young Japanese without localized lesions in the upper gastrointestinal tract. Findings in 75 specimens obtained from subjects in the 1970s were compared with those of 98 specimens obtained from subjects in the 1990s. The prevalence of H. pylori infection in the 1970s (54.7%) was significantly higher than that in the 1990s (28.6%) (p < 0.01). The grade of inflammation and the prevalence of both mucosal atrophy and intestinal metaplasia also were significantly higher in the 1970s than in the 1990s (p < 0.01 and p < 0.05). Our data thus show a trend toward a reduced prevalence of H. pylori infection and of histologically apparent gastritis (especially atrophic gastritis). This decrease may be linked to the reported decline of gastric carcinoma in Japan.