INTRODUCTION: We aimed to assess the validity of the schizophrenia diagnoses registered in the Danish Schizophrenia Registry (DSR) by comparing with information from medical records. METHODS: The study included a random sample of 390 subjects from the DSR who were representative of each geographic region of Denmark. For each subject in the sample, a medical record review was performed by local psychiatrists to confirm or disconfirm the schizophrenia diagnosis and to give a qualified estimate of the date of diagnosis. Only register data and medical record information were used, and thus the individuals in the sample were not approached. We calculated the positive predictive value, comparing registrations in the DSR with the original medical records as a reference. RESULTS: A total of 325 out of 390 (83%) medical records were reviewed. The positive predictive value was 91% (95% confidence interval (CI): 88-94%), varying between geographic regions from 85% to 100%. The classification of incident versus prevalent disease corresponded with the reference in 93% (95% CI: 80-97%) of cases diagnosed in 2014-2015. CONCLUSIONS: The DSR includes the intended patient population and represents a valid and valuable source for improving quality of care and for research.