This research examined the prevalence of comorbid borderline personality disorder (BPD) in a sample of schizophrenia inpatients, and then investigated the degree to which BPD comorbidity impacted symptom and functional outcomes after 1-year post-hospital discharge. A sample of 142 individuals with a diagnosis of schizophrenia (n = 100) or schizoaffective disorder (n = 42) from the MacArthur Violence Risk Assessment Study were administered the Structured Interview for DSM-III-R Personality (SIDP-R). Symptom and functional outcome data were gathered during hospitalization and at 1-year follow-up to analyze differences in symptom and functioning characteristics between those diagnosed with and without BPD. Results indicated that comorbid BPD was present in a non-trivial proportion (17.6%, n = 25) of the sample, based on SIDP-R assessment. Baseline analyses indicated that patients with BPD presented with modest elevations in the severity of overall psychiatric symptomatology, and higher levels of anxiety and depression, at hospitalization compared to non-BPD patients. At 1-year follow-up, results revealed that after adjusting for baseline differences, patients with schizophrenia and comorbid BPD showed significantly less improvement in psychiatric symptomatology, particularly hostility and suspiciousness, as well as global functioning, and were re-hospitalized at significantly higher rates than patients without BPD. Our findings indicate that the co-occurrence of schizophrenia and BPD is not infrequent and that BPD has a significant negative longitudinal impact on the course and outcome of patients with schizophrenia.