Serial histological specimens from 14 patients with the endoscopic diagnosis of erosive gastritis and/or duodenitis were examined for correlation between endoscopic and histological findings. All patients were symptomatic outpatients without history of alcoholism or usage of aspirin or nonsteroidal antiinflammatory drugs. After the initial diagnosis, the patients underwent follow-up endoscopy until healing of erosions at 1, 4, and 8 wk. Pairs of biopsies from the gastric fundus, body, and antrum, and the duodenum were obtained at each endoscopy. Agreement between histological and endoscopic findings occurred in only 56% of the 161 sites studied. The best correlation occurred in the duodenum when there was endoscopic disease (89%) and was worst in the stomach at all sites regardless of endoscopic findings (46%). A normal histology in the face of abnormal endoscopic changes was seen in only 16% of all biopsies. Histological inflammation occurred in 27% of all biopsies with a normal endoscopic appearance and in 55% of the normal endoscopic areas in the stomach. Histological appearances at each biopsy site remained constant in individual patients throughout the study. The specific histological findings, such as activity and severity, did not correlate with the endoscopic severity of inflammation or with any specific endoscopic appearances, such as erosions, petechiae, or nodules. In conclusion, the histological and endoscopic findings in the stomach from patients with symptomatic erosive gastroduodenitis correlate poorly while good correlation occurs in the duodenum.