ABSTRACT Purpose To evaluate differences in the incidence of ocular complications among pediatric and young adult patients with non-infectious uveitis receiving immunosuppressive therapy (IMT), according to the time from uveitis onset to IMT initiation in Japan. Methods Patients aged < 20 years exhibiting uveitis treated with IMT (e.g. methotrexate, cyclosporine, infliximab, or adalimumab) were categorized into three groups according to the time from uveitis onset to IMT initiation: ≤6 months, early IMT group; 7 months to 2 years, intermediate IMT group; and ≥ 2 years, late IMT group. The percentage of ocular complications was compared among these groups. Laser flare values were recorded to evaluate disruption of the blood-aqueous barrier (BAB). Results Forty-three patients (84 eyes) who received IMT during the follow-up period were included. Among them, 28 patients (65.1%) experienced ≥ 1 ocular complication, with percentage of 56.0% in the early IMT group, 77.8% in the intermediate group, and 77.8% in the late group. Common complications were cataract (27.4%), posterior synechiae (17.9%), and macular edema (10.7%). The early IMT group did not require surgical intervention. The late IMT group experienced a high percentage of ocular complications despite IMT initiation. The mean laser flare value during follow-up was consistently higher in the late group (113.2 pc/ms) than in the early group (14.4 pc/ms) and intermediate group (28.7 pc/ms). Conclusion In pediatric and young adult patients with chronic non-infectious uveitis, early IMT initiation may prevent permanent breakdown of the BAB, reduce the incidence of ocular complications, and decrease the need for surgical intervention.