Barrett's esophagus in children and young adults. Frequent association with mental retardation. Since few data are available on epidemiologic features of Barrett's esophagus in young persons, we reviewed the case records of patients undergoing esophageal biopsies at Children's Hospital, Boston, from 1982 through 1986. There were 1423 esophageal biopsies obtained from 1173 patients, and histological evidence of esophagitis was present in 397 cases; Barrett's epithelium was diagnosed in 10 patients (0.9% of total and 2.5% of esophagitis cases). Specialized columnar epithelium was present in seven of these 10 patients. The mean age of those with Barrett's epithelium was 19.0 +/- 7.9 years (range 3.7-27 years) compared to 8.7 +/- 6.7 years (range 4 days to 31 years) for all patients biopsied (P less than 0.0001); 80% (8/10) of the Barrett's cases were male compared to 54% of all cases. The relative importance of the possible risk factors was assessed by comparing the 10 patients with Barrett's with the 541 patients that had esophageal biopsies in calendar years 1984-1985. Mental retardation, a risk factor not previously described for young persons with Barrett's esophagitis, was present in 70% (7/10) of the Barrett's patients but in only 15% of all patients biopsied (P less than 0.0002). The frequency of mental retardation was also higher, but not significantly so (P greater than 0.07), in patients with biopsies that were positive for esophagitis (19%) than in those with normal biopsies (14%). No significant differences were found between the Barrett's group and all patients biopsied in regards to racial origin, prior stricture, or fundoplication. 