The authors determined the risk for psychiatric disorders in the first-degree relatives of 36 probands with schizotypal personality disorder (13 definite, 23 probable), 17 probands with borderline personality disorder (two definite, 15 probable), and 90 normal control probands. The relatives of probands with schizotypal personality disorder without a concurrent diagnosis of borderline personality disorder had a significantly greater risk for schizotypal personality disorder than the relatives of normal control probands, borderline probands, or schizotypal probands with coexisting borderline personality disorder. The relatives of borderline probands had a significantly greater risk for definite and probable borderline personality disorder than the relatives of normal control probands.