• A comparison was made of the types of mental disorders occurring in the first-degree relatives of 83 female patients with DSM-III borderline personality disorder, 100 female patients with DSM-III schizophrenia, and 100 female patients with DSM-III bipolar disorder. Diagnosis of the relatives was made independently by two clinicians who were blind to the diagnosis of the probands. The relative of a borderline patient was about ten times more likely to have been treated for a borderline or borderlinelike personality disorder than was the relative of a schizophrenic or bipolar patient. The borderline patients' relatives were also treated for more unipolar depression than the schizophrenics' relatives. However, the relatives of the borderline patients did not have a higher morbid risk for treated mania or schizophrenia than that usually reported for the population at large.