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BACKGROUND:The Danish National Lymphoma Register (LYFO) prospectively includes information on all lymphoma patients newly diagnosed at hematology departments in Denmark. The validity of the clinical information in the LYFO has never been systematically assessed. AIM:To test the coverage and data quality of the LYFO. METHODS:The coverage was tested by merging data of the LYFO with the Danish Cancer Register and the Danish National Patient Register, respectively. The validity of the LYFO was assessed by crosschecking with information from medical records in subgroups of patients. A random sample of 3% (N = 364) was made from all patients in the LYFO. In addition, four subtypes of lymphomas were validated: CNS lymphomas, diffuse large B-cell lymphomas, peripheral T-cell lymphomas, and Hodgkin lymphomas. A total of 1,706 patients from the period 2000-2012 were included. The positive predictive values (PPVs) and completeness of selected variables were calculated for each subgroup and for the entire cohort of patients. RESULTS:The comparison of data from the LYFO with the Danish Cancer Register and the Danish National Patient Register revealed a high coverage. In addition, the data quality was good with high PPVs (87% to 100%), and high completeness (92% to 100%). CONCLUSION:The LYFO is a unique, nationwide clinical database characterized by high validity, good coverage and prospective data entry. It represents a valuable resource for future lymphoma research.