The purpose of this study was to determine the incidence and risk factors of hypotony and the effectiveness of medical and surgical treatment. A total 117 eyes of 103 patients that underwent trabeculectomy with mitimycin C (MMC) between 1993 and 2000 were reviewed. Hypotony was treated with the following methods in a stepwise manner: medical treatment, intrableb autologous blood injection, additional sutures to the scleral flap, necrotic bleb excision and advancement of the forniceal conjunctival flap. Hypotony developed in 30 eyes (25.6%) of 26 patients, among, which hypotonic maculopathy developed in 11 eyes (9.4%). The risk factors of hypotony were young age and primary open angle glaucoma. Because of no light sense, 6 of the 30 hypotonic eyes were not treated. Nineteen (79.2%) of the 24 treated hypotonic eyes were successfully managed. Five eyes, 3 with hypotony but maintaining visual acuity and 2 with follow-up loss, were not included in the success group. The mean intraocular pressure (IOP) before treatment, 2.5 ± 1.2 mmHg, increased to 8.3 ± 4.0 mmHg at 18.5 months follow-up. The stepwise treatment seems to be a useful method to manage hypotony after trabeculectomy with MMC.