This study evaluated the validity of the ICD-10 diagnostic codes for aortic dissections (ADs) in the Danish National Patient Registry (DNPR) based upon positive predictive values (PPV).Cases registered in the DNPR with the unspecific AD diagnostic code DI710 (unspecified AD) from 1996 to 2016, and the specific AD diagnostic codes DI710A (AD Type A) and DI710B (AD Type B) from 2006 to 2016, were included. Available medical records from all registered cases underwent review. Confirmed cases of AD served as "gold standard" when reporting PPV. PPV estimates were stratified by regional differences, date, age at time of diagnosis, and sex.A total of 5018 cases were identified in the DNPR. After merging of data and retrieval of medical records, 3767 cases were eligible for validation. Of these, 2677 cases were verified as AD type A (59.7%), AD type B (38.8%), and unspecified type of AD (1.5%). The average age at diagnosis was 65.1 ±13.0 years (67.3% males). The overall PPV for having an AD when one of the three diagnostic codes were registered from 1996 to 2016 was 71.1% (95% confidence interval (CI): 69.6-72.5) and increased significantly over time. From 2006 to 2016, the PPV for the specific AD diagnostic codes was 89.5% (95% CI: 87.4-91.3), whilst the PPV for the unspecific diagnostic code was 63.5% (95% CI: 61.1-65.9).We found the overall PPV for the pooled AD diagnostic codes in the DNPR acceptable. However, the two specific AD diagnostic codes presented remarkably higher PPV compared to the unspecific diagnostic code.