The Cohen syndrome is a genetic disorder consisting of mental retardation, obesity, hypotonia, and a characteristic craniofacial appearance. Since its original description, 13 patients have been reported. This presentation gives an account of 5 additional cases in 4 families and provides further evidence that this disorder is most probably transmitted as an autosomal recessive trait. This study also demonstrates the range of clinical features observed in this syndrome and suggests that the basic defect may be one of connective tissue.