Purpose To compare the clinical outcomes of the EX-PRESS glaucoma filtration device placed under a partial-thickness scleral flap with trabeculectomy. Design Randomized, prospective, multicenter trial. Methods A total of 120 eyes in 120 subjects were analyzed, including 59 eyes treated with EX-PRESS and 61 eyes treated with trabeculectomy. Both the EX-PRESS and the trabeculectomy groups were treated intraoperatively with mitomycin C and followed postoperatively for 2 years. Surgical success was defined as 5 mm Hg ≤ intraocular pressure ≤ 18 mm Hg, with or without medications, without further glaucoma surgery. Results Mean intraocular pressure was significantly reduced compared with baseline in both groups (P < 0.001). Average intraocular pressure and number of medications were similar in both groups during follow-up, with mean intraocular pressure at 2 years after surgery of 14.7 ± 4.6 mm Hg and 14.6 ± 7.1 mm Hg in the EX-PRESS and trabeculectomy groups, respectively (P = 0.927). At 2 years after surgery, the success rate was 83% and 79% in the EX-PRESS and trabeculectomy groups, respectively (P = 0.563). Although visual acuity (logMAR) was significantly decreased on day 1 in both groups, the vision was not significantly different compared with baseline at 1 month after EX-PRESS implant (P = 0.285) and 3 months after trabeculectomy (P = 0.255). The variance of early postoperative intraocular pressure values was similar between groups on the first postoperative day but higher after trabeculectomy compared with EX-PRESS implant on day 7 (P = 0.003). The total number of postoperative complications was higher after trabeculectomy than after EX-PRESS implantation (P = 0.013). Conclusions Mean intraocular pressures, medication use, and surgical success were similar at 2 years after treatment with the EX-PRESS device and trabeculectomy. Vision recovery between groups was also similar throughout the study, although return to baseline vision was more rapid in the EX-PRESS group. Intraocular pressure variation was lower during the early postoperative period, and postoperative complications were less common after EX-PRESS implantation compared with trabeculectomy.