Barrett's esophagus is a premalignant condition defined by the presence of intestinal metaplasia in the esophagus. Estimates of the incidence of adenocarcinoma developing in patients with Barrett's esophagus vary widely. We prospectively followed a cohort of patients to define the incidence. Between January 1982 and April 1995, all patients undergoing upper endoscopy at the VA Medical Center in Tucson, AZ, were surveyed for Barrett's esophagus. One hundred seventy-seven patients (174 males, three females) were found to have Barrett's esophagus. Seven of 177 were found to have adenocarcinoma either at initial endoscopy or within 6 months, resulting in a prevalence of 4%. One hundred seventy of 177 patients initially lacking cancer were available for systematic survey. The mean age at the time of Barrett's diagnosis was 62 yr (range 30-85 yr). The mean follow-up period was 57 months or 4.8 yr (range 6-156 months), for a total of 834 patient-years. Adenocarcinoma developed in four patients, an incidence of 1/208 patient-years of follow-up. The current series is larger and has a longer follow-up period than previous prospective trials and demonstrates a lower incidence of adenocarcinoma. Surveillance of patients with Barrett's esophagus for dysplasia remains an appropriate clinical practice.