There was moderate-excellent inter-rater reliability for most cohorts in this sample. There was sufficient disagreement, however, particularly for the schizoaffective cohort, to suggest the value of applying a standardized and structured assessment approach to psychiatric diagnosis. A standardized approach would likely enhance both the accuracy of diagnosis and the prospective validity of tissue-based research. The present study also highlights the importance of accurate and detailed medical record keeping at a symptom-based level across all mental health professions. In the absence of clear and adequate symptom-based detail, the reliability of both ante-mortem and post-mortem diagnosis may be compromised.