Purpose To assess the nationwide rate of acute postoperative endophthalmitis (APE) after cataract extraction in Korea and to evaluate potential risk factors thereof. Materials and Methods Nationwide insurance claims data from July 2014 to June 2017 were reviewed. All patients with phacoemulsification or extracapsular/intracapsular cataract extraction were included. Exclusion criteria were combined glaucoma surgery or total vitrectomy or when the patient had a history of intraocular foreign body. Results In total, 1505103 cases (982203 patients) were included. APE developed in 953 cases (938 patients) with an overall incidence of 0.063%. After adjusting for possible confounding factors, male sex [odds ratio (OR) 1.42; 95% confidence interval (CI) 1.25–1.61; p <0.001], primary clinical setting, operations performed in non-major cities, usage of sutures (OR 2.82; 95% CI 2.13–3.74; p <0.001), anterior vitrectomy (OR 8.71; 95% CI 6.71–11.32; p <0.001), aphakic cataract surgery (OR 1.52; 95% CI 1.03–2.22; p =0.033), hypertension (OR 1.40; 95% CI 1.18–1.66; p <0.001), diabetes (OR 1.59; 95% CI 1.31–1.93; p <0.001), and chronic renal failure (OR 1.28; 95% CI 1.01–1.62; p =0.039) were found to be related to APE development. Conclusion The incidence of APE after cataract extraction was consistent with reports from other studies. Additional research is needed to determine the relationship of newly found risk factors, such as hypertension, primary clinical setting, chronic renal failure, and usage of suturing, with APE development.