This study investigated similarities and differences in the experience of auditory hallucinations, paranoia, and childhood trauma in schizophrenia and borderline personality disorder (BPD). Patients with clinical diagnoses of schizophrenia or BPD were interviewed using the Structured Clinical Interviews for DSM-IV. Axes 1 and 2 and auditory hallucinations, paranoia, and childhood trauma were assessed. A total of 111 patients participated; 59 met criteria for schizophrenia, 33 for BPD, and 19 for both. The groups were similar in their experiences of voices, including the perceived location of them, but they differed in frequency of paranoid delusions. Those with a diagnosis of BPD, including those with schizophrenia comorbidity, reported more childhood trauma, especially emotional abuse. BPD and schizophrenia frequently coexist, and this comorbidity has implications for diagnostic classification and treatment. Levels of reported childhood trauma are especially high in those with a BPD diagnosis, whether they have schizophrenia or not, and this requires assessment and appropriate management.