Purpose: The Danish Shoulder Arthroplasty Registry (DSR) is a nationwide database provid-ing data for research and health care monitoring. The aim of this study was to validate the DSR by (1) assessing registration completeness, (2) comparing key variables with information from medical records, (3) assessing the number and proportion of missing data for key variables. Materials and Methods: The completeness of registration in the DSR from 2006–2015 was assessed for primary arthroplasties by comparing the number of arthroplasties reported to the DSR with the number of arthroplasties recorded by the Danish National Patient Register which is an administrative database used by the Danish healthcare authorities to monitor all hospitalizations including shoulder arthroplasty surgery. Positive predictive values (PPV) were used to estimate the accuracy of the reporting in a randomly selected population. Information retrieved from medical records were used as gold standard. The number of missing values for each variable was evaluated to depict if these registrations were missing at random. Results: The completeness of reporting was 94.4. The PPV for the three major indications: osteoarthritis, fracture and rotator cuff arthropathy was 92%, 97%, and 94%, respectively. PPV was high for resurfacing arthroplasty (93%) and reverse shoulder arthroplasty (93%), but low for total shoulder arthroplasty (79%) and hemiarthroplasty (83%). The proportion of missing data in DSR was less than 1% for age, gender, previous surgery, indication and arthroplasty type and these can be regarded as missing at random. Conclusion: The study showed that data from the DSR are sufficiently valid to be used for research and quality monitoring. Lower PPV’s for total shoulder arthroplasty and hemiar-throplasty are possibly related to inadequate definitions and mutually nonexclusive items in the reporting form. Regular validation is necessary since the data reported to the registry continuously evolve because of changes in clinical practice.