Background: Alopecia areata (AA) is a common inflammatory condition affecting hair, but epidemiologic study on the disease, especially in Asia, is rare and offers inconsistent results from one study to another. Objectives: To investigate the prevalence and incidence of AA, including alopecia totalis (AT) and alopecia universalis (AU), and to clarify their demographic distribution. Methods: We analyzed a nationwide representative sample cohort of over one million South Koreans using data from the National Health Insurance Service-National Sample Cohort from 2002 to 2013. Results: Overall incidence and prevalence during the study period was 98.5 (95% confidence interval (CI), 96.6-104.4) and 154.6 (95% CI, 134.9-174.3), respectively. Overall increases were seen in both of these measures during the period. The mean prevalence of AT per 100,000 persons was 3.7 (95% CI, 3.5-3.9), and the prevalence rate of AT per 100 AA patients was 2.4 (95% CI, 2.2-2.7). The mean prevalence of AU per 100,000 persons was 0.9 (95% CI, 0.7-1.1) and the prevalence rate of AU per 100 AA patients was 0.6 (95% CI, 0.5-0.7). The age distribution resembled a bell shaped curve peaking at ages from 30 to 39 for both the AA and AU or AT combined. Conclusion: This is the first nationwide population-based, epidemiologic study of AA in the Asian population. Our result demonstrates an increase in the frequency especially in milder form of AA in South Korea, contributing to a greater appreciation of the disease burden.