Three interviewers (second raters) blindly rated 15 audiotapes each of the Structured Clinical Interview for DSM-III-R, Axis II (SCID-II) administered to the first degree relatives of probands with either DSM-III-R schizophrenia, schizoaffective disorder, or bipolar disorder, for a total of 45 second ratings. Interrater reliability was determined using the intraclass correlation coefficient and ranged from 0.60 to 0.84. The previous studies of the reliability of structured interviews for diagnosing personality disorders are summarized and compared to the present findings. We conclude that the SCID-II can be reliably used to diagnose schizophrenia-spectrum and affective spectrum disorders in the first degree family members of probands with schizophrenic or bipolar affective disorders.