Background: Gastrointestinal and respiratory symptoms and failure to thrive not associated with infections or medications were noted in patients with severe combined immunodeficiency. Objective: The aim of our study was to determine the frequency of gastroesophageal reflux in patients with severe combined immunodeficiency.Methods: We studied the case histories of 73 pediatric patients who had been treated at Duke University Medical Center for severe combined immunodeficiency between 1982 and 1995. Charts were reviewed for documentation of gastroesophageal reflux on the basis of clinical course and results of barium swallow esophageal pH probe monitoring, or endoscopy. To compare the incidence of gastroesophageal reflux in patients with severe combined immunodeficiency to known high-risk populations, we additionally tabulated the underlying diagnoses in an age-matched group of patients who underwent Nissen fundoplication from 1990 to 1995. Results: We found clinically significant gastroesophageal reflux in 15 of the 73 patients (20.5%), much higher than has been reported in the normal population (0.1% to 0.3%, p < 0.001). Of patients treated between 1990 and the present, 10 of 36 (27.7%) had significant gastroesophageal reflux compared with five of 37 patients (13.5%) in the previous years. Thus with greater recognition and improved methods for diagnosis, the observed incidence of gastroesophageal reflux has increased greatly. The clinical presentations were not different from those of patients with other well-documented underlying diagnoses. Seven of the 15 patients (46.6%) did not respond to medical treatment with antacids, H-2-blockers, and prokinetic agents and underwent surgical treatment. Indications for surgery included persistent esophagitis, vomiting, pneumonia, and growth failure. Conclusions: The reason for the high incidence of gastroesophageal reflux in patients with severe T-cell disorders remains unclear. Considering the frequency of this association, early recognition and treatment is important to enable adequate nutrition and prevent damage to the esophagus and lungs.