Fragile X (or Martin-Bell) syndrome, a common, genetic, mental retardation disorder is increasingly being recognized as a major cause of cognitive disability and psychiatric illness in boys. Here, we present a study in which relatives in 4 generations of a large family with the fra(X) chromosome were given comprehensive psychiatric evaluations in order to further describe the psychopathology associated with this condition. Three of 4 males with the fra(X) chromosome were found to have autistic behavior. An adult fra(X) male had a chronic schizoaffective disorder and mental retardation. In female relatives, a relationship was found between the fra(X) carrier status and psychopathology including schizoaffective and major affective disorders.