A pair of male monozygous twins of gynandromorphic habitus but normal male body hair and genitalia, who appear concordant for transsexualism and explosive personality disorder but discordant for schizophrenia, is presented. No evidence of specific family dynamic factors, imitative learning or folie a deux was found in the twins' history. A constitutional aetiology of their transsexualism and one twin's schizophrenia is suggested. The relationship between transsexualism and schizophrenia is briefly reviewed. No evidence can be found that the modal transsexual is suffering from a schizophrenic disorder, florid or attenuated. A more subtle relationship is possible of transsexualism occurring as a schizophrenic spectrum disorder. This twin pair appears to illustrate such a relationship.