This study is a review of our patients with gastroesophageal reflux who were severely retarded. Twelve mentally retarded patients who had undergone Nissen fundoplication and pyloroplasty during a period from 1980 through 1989 are the subjects of this study. Eight patients had cerebral palsy, two had Cornelia de Lange syndrome, one had West syndrome and the other had multiple minor anomalies. Eight patients were badly undernourished and their body weights were more than 2.7 standard deviations below the mean value. Vomiting stopped in ten patients after surgery, but wheezing persisted in three of them. Weight gain was observed in eight patients. Three patients have died from unknown causes. This study suggests : (1) Severely retarded children are at high risk of developing gastroesophageal reflux. Nissen fundoplication with pyloroplasty is effective treatment. The protective anti-reflux operation should be carried out when a tube gastrostomy is to be placed in them. (2) The patients often have hypertrophy of the left lobe of the liver, kypho-scoliosis and/or a ventricular-peritoneal shunt, which make the operation awkward.(3) Careful obsevation after surgery must be carried out.