This study aimed to evaluate the incidence of clinically significant intraocular inflammation (csIOI) after treatment with intravitreal injection (IVI) of brolucizumab and identify csIOI risk factors. We categorized 60,966 South Korean patients from a nationwide population-based cohort into 4 groups: groups 1 (Ranibizumab), 2 (Aflibercept), 3 (Brolucizumab), and 4 (switched to brolucizumab). We used the Kaplan–Meier method to estimate the cumulative incidence of csIOI in each group and calculated the hazard ratios (HRs) and 95% confidence intervals (CIs). We constructed a multivariate model using forward selection methods to identify risk factors for csIOI. The cumulative incidence of csIOI within 180 days of the index date in groups 1, 2, 3, and 4 was 0.36% (67/18,537), 0.49% (186/37,951), 3.47% (38/1,095), and 3.69% (125/3,383), respectively. Multivariate analysis revealed a significant increase in csIOI risk in groups 3 (HR 11.08, 95% CI 7.42–16.53, P < 0.001) and 4 (HR 10.40, 95% CI 7.67–14.09, P < 0.001). History of retinal vascular occlusion (HR 1.56, 95% CI 1.01–2.40, P = 0.043) significantly increased csIOI risk after brolucizumab IVI treatment; female sex (HR 0.78, 95% CI 0.64–0.96, p = 0.020) and diabetes (HR 0.72, 95% CI 0.58–0.90, p = 0.004) decreased the risk. csIOI incidence was higher after brolucizumab IVI treatment than after ranibizumab and aflibercept IVI treatment. Retinal vein occlusion history, female sex, and diabetes are associated with csIOI after brolucizumab IVI treatment.