ABSTRACT: BACKGROUND:Despite the significant disease burden, there is a paucity of data addressing the population-based incidence of acute angle closure glaucoma (AACG). Therefore, we estimated the nationwide, population-based standardized incidence rate of AACG in Korea. METHODS:We conducted a nationwide, population-based, retrospective study using the database of National Health Insurance (NHI) system, which includes the entire Korean population (approximately 50 million people) from 2009 to 2015. We identified patients with incident AACG during the 5-year study period from 2011 to 2015 based on their diagnosis and AACG-related treatments (laser iridotomy and cataract surgery), and estimated age- and gender-standardized incidence rate of AACG during the study period. RESULTS:We identified 11,049 patients (8,022 women, 72.6%) with incident AACG during the 5-year study period. Of these, after excluding 6 patients under 20 years old, 11,043 patients (8,020 women, 72.6%) aged ? 20 years were included in the analysis. The average standardized incidence rate during the 5-year study period was 59.95 (95% confidence interval [CI], 58.87-61.03) per 1,000,000 person-years. The incidence rates increased sharply with age and peaked at individuals aged 75-79 years; in men, those peaked at the same age group, however, in women, those peaked at individuals aged 70-74 years. Women has a 2.56 folds higher incidence rate (85.84 [95% CI, 84.03-87.66] per 1,000,000 person-years) than men (33.48 [95% CI, 32.33-34.62] per 1,000,000 person-years). CONCLUSION:The present study provides detailed estimates for AACG incidence according to all age groups and gender through the 5-year study period.