Marie Bak,1 Else Helene Ibfelt,2 Thomas Stauffer Larsen,3 Dorthe Rønnov-Jessen,4 Niels Pallisgaard,5 Ann Madelung,6 Lene Udby,1 Hans Carl Hasselbalch,1 Ole Weis Bjerrum,7 Christen Lykkegaard Andersen1,7 1Department of Hematology, Zealand University Hospital, University of Copenhagen, Roskilde, 2Research Centre for Prevention and Health, Rigshospitalet Glostrup, University of Copenhagen, Glostrup, 3Department of Hematology, Odense University Hospital, Odense, 4Department of Hematology, Vejle Hospital, Vejle, 5Department of Surgical Pathology, Zealand University Hospital, University of Copenhagen, Roskilde, 6Department of Surgical Pathology, Zealand University Hospital, University of Copenhagen, Næstved, 7Department of Hematology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark Aim: The Danish National Chronic Myeloid Neoplasia Registry (DCMR) is a population-based clinical quality database, introduced to evaluate diagnosis and treatment of patients with chronic myeloid malignancies. The aim is to monitor the clinical quality at the national, regional, and hospital departmental levels and serve as a platform for research. Study population: The DCMR has nationwide coverage and contains information on patients diagnosed at hematology departments from January 2010 onward, including patients with essential thrombocythemia, polycythemia vera, myelofibrosis, unclassifiable myeloproliferative neoplasms, chronic myelomonocytic leukemia, and chronic myeloid leukemia. Main variables: Data are collected using standardized registration forms (so far up to four forms per patient), which are consecutively filled out online at time of diagnosis, after 2-year and 5-year follow-ups, and at end of follow-up. The forms include variables that describe clinical/paraclinical assessments, treatment, disease progression, and survival – disease-specific variables – as well as variables that are identical for all chronic myeloid malignancies. Descriptive data: By the end of 2014, the DCMR contained data on 2,690 patients with an inclusion rate of ~500 patients each year. Since the registry was established, annual reports have shown consistently high national coverage and data completeness, ≥90% and ≥88%, respectively. Conclusion: The DCMR is a national database used for monitoring the quality of patient care in patients with chronic myeloid malignancies, but until validation has been conducted, the data must be used with caution. However, the DCMR is a valuable data source accessible to clinicians and researchers. Keywords: myeloproliferative disorders, database, treatment, health care quality assurance, outcome assessment, epidemiology, research