Psychotic illness was associated with an apparently balanced 6;11 chromosomal translocation in a three-generation family. The mother and son carrying the translocation suffer from a chronic psychotic illness, a daughter who was a translocation carrier committed suicide, and her twin daughters who both carry the translocation have not yet reached the age of risk for developing this psychiatric illness, although one has attempted suicide. Two older members of the family have the translocation and have never suffered from a psychiatric disorder. The pattern of dominant inheritance of the psychotic illness only occurring in individuals carrying the translocation suggests that there may be a major genetic component in the etiology of the psychosis in this family. Genes at the chromosomal break points may be candidate genes implicated in this particular form of psychotic illness.