Two brothers presented from birth with features characteristic of Sotos syndrome (cerebral gigantism): overgrowth, craniofacial abnormalities, and mental retardation with hyperactive and aggressive behavior. X-ray examination of the hands revealed imbalanced and advanced skeletal age in one, whereas anterior fontanel bones were present in both brothers. Various hormone concentrations in plasma were all within normal limits, as were the results of a search for abnormal metabolites in plasma and urine. The occurrence of this usually sporadic syndrome in two sons of possible remotely consanguineous, healthy parents, suggests that in some cases Sotos syndrome may be inherited as an autosomal recessive trait. Thus our observation may support the suggestion of heterogeneity of Sotos syndrome. Until specific tests for the identification of various types are available, genetic counseling for this syndrome is difficult.