Using three sets of clinical criteria to define borderline personality disorder (BPD), P300 (P3) and other long-latency auditory event-related electroencephalographic potentials were measured in 22 subjects with BPD, 32 subjects with other personality disorders, 29 schizophrenics, 22 depressives, and 74 volunteer controls. The patients with BPD were found to differ from patients with nonborderline personality disorders, having a longer P3 latency and smaller P3 amplitude. Long-latency event-related potentials were similar in the BPD and schizophrenic groups and did not differentiate patients with BPD with a concurrent diagnosis of schizotypal personality disorder from those without schizotypal personality disorder. The P3 latency and amplitude changes distinguished the BPD and schizophrenic groups from normal controls, those with major depressive disorder, and those with nonborderline personality disorders. These findings suggest that though some patients with BPD may have depressive symptomatology, they share with schizophrenics a dysfunction of auditory neurointegration.