Abstract Purpose To evaluate the safety and intraocular pressure (IOP)-lowering effect of a biodegradable bimatoprost sustained-release implant (Bimatoprost SR). Design Phase I/II, prospective, 24-month, dose-ranging, paired-eye controlled clinical trial. Methods At baseline following washout, open-angle glaucoma patients (n=75) were administered Bimatoprost SR (6-μg, 10-μg, 15-μg, or 20-μg) intracamerally in the study eye; the fellow eye began topical bimatoprost 0.03% QD. Rescue topical IOP-lowering medication or a single repeat treatment with implant was allowed. The primary endpoint was IOP change from baseline. The main safety measure was adverse events. Results through month 6 are reported. Results Bimatoprost SR provided rapid, sustained IOP lowering. Overall mean IOP reduction from baseline through week 16 in study eyes was 7.2, 7.4, 8.1, and 9.5 mm Hg with the 6-μg, 10-μg, 15-μg, and 20-μg dose strengths of implant, respectively, versus 8.4 mm Hg in topical bimatoprost-treated pooled fellow eyes (data censored at rescue/retreatment). Rescue/retreatment was not required in 91% and 71% of study eyes up to week 16 and month 6, respectively. Adverse events in study eyes usually occurred within 2 days after the injection procedure and were transient. Conjunctival hyperemia with onset later than 2 days after the injection procedure was more common with topical bimatoprost than Bimatoprost SR (17.3% vs. 6.7% of eyes). Conclusions Bimatoprost SR demonstrated favorable efficacy and safety through 6 months. All dose strengths were comparable to topical bimatoprost in overall IOP reduction through week 16. A single administration controlled IOP in the majority of patients for up to 6 months.