Introduction: Borderline personality disorder (BPD) and schizotypal personality disorder (SPD) were introduced in DSM-III and retained in DSM-5 Section II. They often co-occur and some aspects of the clinical differentiation between the 2 diagnoses remain unclear (e.g., psychotic-like features and identity disturbance). Methods: The present study explored if self-reported identity disturbance and psychosis proneness could discriminate between the BPD and SPD DSM-5 diagnoses. All patients were interviewed with the Schedules for Clinical Assessment in Neuropsychiatry and the Structured Clinical Interview for DSM-5 Personality Disorders, and administered the Inventory of Personality Organization, Self-Concept and Identity Measure, Schizotypal Personality Questionnaire, Perceptual Aberration Scale, and the Magical Ideation Scale. Results: A total of 105 patients were initially assessed, 26 were excluded, and the final sample (N = 79) was composed of 34 BPD patients, 25 SPD patients, and 20 patients with co-occurring SPD and BPD. The BPD group (n = 34) was first compared with the pure SPD group (n = 25), and secondly with the total group of patients diagnosed with SPD (n = 25 + 20). Logistic regression analyses indicated that primitive defenses and disorganization best differentiated the BPD and the pure SPD group, while primitive defenses and interpersonal factor along with perceptual aberrations best differentiated the BPD and the total SPD group. Conclusion: Identity disturbance did not predict the diagnostic groups, but BPD patients were characterized by primitive defenses, which are closely related to identity disturbance. Pure SPD was characterized by oddness/eccentricity, while the lack of specificity for cognitive-perceptual symptoms suggests that the positive symptoms do not differentiate BPD from SPD.