Twelve sets of triplets, comprising 33 surviving and three stillborn individuals, were incidentally included, along with over a thousand pairs of twins, collected for the purpose of a study of the etiology of mental disorders. The twins and triplets were selected on the basis of at least one in each pair or set having a mental disorder.Neuropsychiatric conditions were found affecting 17 of the 33 subjects, consisting of subnormal intelligence with or without the following complications: child behavior difficulties, juvenile delinquency, adult criminality, psychotic disease and epilepsy.Comparisons of the monozygotic with the dizygotic pairs of subjects among the triplets have failed to reveal any significant contrast with respect to frequency of concordance.The findings yielded by this material, though limited in amount, serve, nevertheless, not only to confirm the conclusions reached by us from our larger-scale studies of twins, but also to further discount the factor of heredity in the etiology of the conditions under consideration.The neuropsychiatric conditions found were all of types which are often seen as residuals or sequels of cerebral birth trauma.Abstract Teaser