AbstractOf 1,235 patients (609 male; 626 female) with congenital heart disease for whom types, etiology and associated congenital anomalies were determinable, 129 patients (10.4%) had mental retardatin. Patients with congenital heart disease complicated by mental retardation included 70 (54.3%) with chromosome aberrations, three(2.3%) with single gene disorders, two (1.6%) caused by environmental insult, and two (1.6%) with other recognized syndromes. Among the remaining 52 patients, asphyxia at birt was noted in 16, including 12 complicated by multiple malformations, and 4 in whom mental retardedation was presumed to be due to the asphyxia. In the remaining 36 patients, the incidence of the complication of mental retardation in cyanotic congenital heart disese was significantly higher than that in acyanotic congenital heart disease was signicantly higher than that in acyanotic congenital heart disease. Patients with congenital heart disease of unknown etiology associated with mental retardation included those from two families considered to have new pedigree syndromes.