A family is reported in which four of five adult patients with Becker muscular dystrophy (BMD) also have schizophrenia or related spectrum disorders. Although the estimated lod scores are not sufficient to conclude the existence of linkage between BMD and schizophrenia, it is suggested that there may be an association between these two disorders. Two alternative hypotheses are proposed to explain such an association: (1) the existence of a susceptibility locus for schizophrenia and spectrum disorders on the short arm of the X chromosome at Xp21; (2) that these psychiatric disorders may result from an abnormality in the expression of the dystrophin gene in the brain.