Osteogenesis imperfecta (OI) is a hereditary connective tissue disease that causes frequent fractures. Little is known about causes of death and length of survival in OI. The objective of this work was to calculate the risk and cause of death, and the median survival time in patients with OI. This study was a Danish nationwide, population-based and register-based cohort study. We used National Patient Register data from 1977 until 2013 with complete long-term follow-up. Participants comprised all patients registered with the diagnosis of OI from 1977 until 2013, and a reference population matched five to one to the OI cohort. We calculated hazard ratios for all-cause mortality and subhazard ratios for cause-specific mortality in a comparison of the OI cohort and the reference population. We also calculated all-cause mortality hazard ratios for males, females, and age groups (0 to 17.99 years, 18.00 to 34.99 years, 35.00 to 54.99 years, 55.00 to 74.99 years, and >75 years). We identified 687 cases of OI (379 women) and included 3435 reference persons (1895 women). A total of 112 patients with OI and 257 persons in the reference population died during the observation period. The all-cause mortality hazard ratio between the OI cohort and the reference population was 2.90. The median survival time for males with OI was 72.4 years, compared to 81.9 in the reference population. The median survival time for females with OI was 77.4 years, compared to 84.5 years in the reference population. Patients with OI had a higher risk of death from respiratory diseases, gastrointestinal diseases, and trauma. We were limited by the lack of clinical information about phenotype and genotype of the included patients. Patients with OI had a higher mortality rate throughout their life compared to the general population.