We studied a nationwide population-based cohort that included all persons born in Denmark between 1955 and 2006, with almost complete follow-up data for up to 57 years. Thus, our findings are unlikely to be explained by biases in the selection of the study population or nondifferentiated attrition during follow-up. However, there are 2 main limitations in this study. First, we used patient registers to identify persons with OCD because it was necessary to use routinely collected data to provide precision for the fairly rare outcomes investigated. Despite a generally acceptable accuracy of diagnoses for mental disorders in the registers,45–51 the included persons treated at hospitals probably have more severe symptoms and greater impairment than do those treated by psychiatrists and pediatricians in private practices. Thus, although our data on OCD diagnoses are of good quality50 and were obtained independently of the outcome, our findings might not be representative of the entire spectrum of OCD but of only those persons with more severe OCD. Second, some of the causes of death may be prone to misclassification. It is possible that some
