Structured clinical interviews of 63 female inpatients diagnosed with borderline personality disorder were used to study the relations of comorbid mood disorders to treatment response. Diagnostic information was gathered using the Structured Clinical Interview for DSM-III-R Personality Disorders (SCID-II) and the Structured Clinical Interview for DSM-III-R-Patient Version (SCID-P). Information about psychotic symptoms was also based upon responses to the SCID-P. Treatment response was assessed through weekly ratings on the Symptom Checklist-90-Revised over 25 weeks of hospitalization. Initial depression but not initial or previous bipolar disorder was found to predict treatment course. Initial psychotic symptoms were also found to predict treatment course among patients with initial bipolar disorder and tended to modify the trajectory of symptoms over time among patients with initial depression. Possible explanations for these findings are explored and discussed.