The comorbidity of depression and borderline disorder was studied in 39 symptomatic borderline inpatients defined by the Diagnostic Interview for Borderlines using three independent methods for assessing depression and three definitions of depression. Evaluations were conducted by the Schedule for Affective Disorders and Schizophrenia interviews for Research Diagnostic Criteria (RDC) depressive disorders, by clinical ratings for atypical depressive disorder, and by self-rated questionnaires for hysteroid dysphoria. Diagnoses of an RDC depression were made in 25 (64.1%), atypical depressive disorder in 16 (41%), and hysteroid dysphoria in 25 (64.1%) of the borderline patients. Two depressive diagnoses were present in 64.1% of patients, while 17.9% of patients met criteria for all three depressive disorders. No one method accurately characterized depression in borderline patients.