The rate of DSM-III schizotypal personality traits was evaluated in three groups of adolescent offspring (ages 15-21), defined by the psychiatric diagnosis of their parents. Parental diagnoses included schizophrenic disorder (40 adolescents), affective disorder (35 adolescents), and 'no psychiatric disorder' (normal controls) parents (82 adolescents). The presence of the eight component features of schizotypal personality disorder was assessed from video-taped semistructured psychiatric interviews, subsequently rated by trained psychiatrists, blind to the parental psychiatric status of the subjects. The effect of age, sex, and social class on the pattern of prevalence results was examined. The expected specificity of DSM-III schizotypal personality traits to schizophrenia was not supported by the prevalence pattern of the traits. Rates of 2 or more, 3 or more, and 4 or more schizotypal personality features were highest in the parental psychiatric groups. The rates of schizotypal personality traits in adolescent offspring of affective disorder parents were as high as those previously reported for relatives of schizophrenic disorder probands.