Objectives To describe the population of patients diagnosed with hypertrophic cardiomyopathy (HCM) in Denmark and determine temporal trends in incidence and patient characteristics over time. Design Nationwide retrospective cohort study. Setting Danish nationwide administrative and clinical registers and databases. Participants All patients aged ≥16 years diagnosed with HCM from 2005 to 2018. Outcomes measures Time trends in HCM diagnosis, patient characteristics, comorbidities and pharmacotherapy were identified and tested for significance using the Cochran-Armitage trend test. Results 3856 HCM patients were included (median age 68 years (IQR 56-78)). Although there were more males (53%), females were older (72 years vs 63 years) and more likely to have their type of HCM classified as obstructive (54% vs 38%). A consistent rise in HCM cases per year was detected and there was a significant decline in prevalence of heart failure (2005: 20% to 2018: 12%, p<0.001) and ischaemic heart disease (2005: 31% to 2019: 16%, p≤0.001). Prevalence of atrial fibrillation and stroke remained notable and unchanged. Lastly, the rate of hospitalisations decreased over time (2005: 64% to 2016: 46%, p<0.001), while the rate of outpatient follow-up increased (2005: 81% to 2016: 87%, p 0.003). Conclusion There was a consistent rise in HCM cases with decreasing morbidity burden. Females were older at diagnosis and more likely to have their type of HCM classified as obstructive. The rate of outpatient follow-up is increasing.