Recent changes in the incidence of duodenal and gastric ulcer.

The incidence of duodenal and gastric ulcer was examined in a Health Maintenance Organization with over 200,000 members. Hospitalization data were available from 1966 through 1975, and outpatient data from 1967 through 1973. Outpatient episodes of duodenal ulcer declined from 21.0 +/- 3.6 episodes per 1000 male person years (PY) in 1967 to 6.6 +/- 1.5 per 1000 male PY in 1973, and from 9.4 +/- 2.4 episodes per 1000 female PY in 1967 to 4.1 +/- 0.8 per 1000 female PY in 1973. Similar declines were observed in the hospitalization data. There were slight declines in gastric ulcer rates, but these were not significant except for a decrease in male gastric ulcer hospitalizations. The decrease in duodenal ulcer incidence has no readily apparent explanation.