Upper gastrointestinal (UGI) tract bleeding is a common reason for hospitalization of mentally retarded adults. The purpose of this study was to determine the frequency and cause of and risk factors for UGI tract bleeding in institutionalized mentally retarded adults admitted to our hospital. Case-control study, with a retrospective review of medical records. Inner-city tertiary care hospital. Mentally retarded adults who reside in one of three long-term care facilities. Data on demographic features, clinical features, and concurrent medical conditions were collected on mentally retarded adults admitted to our hospital for UGI tract bleeding (n = 40). Data from these patients were compared with those from a control group of mentally retarded adults admitted for nonbleeding conditions (n = 124). Endoscopic data were reviewed on the patients who bled to further clarify the causes of UGI tract bleeding. The patients who bled were compared with those who did not bleed using the chi 2 and Mann-Whitney rank sum tests. Upper gastrointestinal tract bleeding was the most common reason for hospitalization in this patient population. Such bleeding was most commonly caused by erosive esophagitis (70% of patients who bled). Conditions associated with an increased risk for UGI tract bleeding were hiatal hernia, reduced activity, incontinence, hypoalbuminemia, kyphoscoliosis, and spastic quadriplegia. Upper gastrointestinal tract bleeding is a common cause of hospitalization in mentally retarded adults and is usually due to erosive esophagitis. It is hoped that vigorous efforts to treat gastroesophageal reflux disease may reduce hospitalization in these patients.