The development of Barrett's esophagus was studied using data from 51,311 patients undergoing upper gastrointestinal endoscopy between 1976 and 1989. Three hundred seventy-seven patients had greater than or equal to 3-cm columnar epithelium in the esophagus and no carcinoma. The prevalence of Barrett's esophagus increased with age to reach a plateau by the seventh decade. Half of the maximum prevalence was reached by age 40 years, the estimated median age of development of the disorder. Unlike prevalence, the mean length of columnar epithelium did not increase with age. No significant change in length was found in 21 patients followed up for a mean of 7.3 years (mean initial length, 8.29 +/- 0.85 cm; mean final length, 8.33 +/- 0.77 cm). The length of columnar epithelium did not increase in the presence of esophagitis or decrease when esophagitis was absent. Mean age at diagnosis of Barrett's esophagus was 63 years without carcinoma and 64 years in a separate group of patients with adenocarcinoma. The data are consistent with a fairly rapid evolution of Barrett's esophagus to its full length with little subsequent change. Barrett's esophagus may develop more than 20 years before the mean age of clinical recognition or the development of esophageal adenocarcinoma.