PURPOSE: To describe the intraoperative and postoperative complications encountered during the first year of follow-up in the Tube Versus Trabeculectomy (TVT) Study. DESIGN: Multicenter randomized clinical trial. METHODS: SETTING: Seventeen clinical centers. STUDY POPULATION: Two hundred twelve patients aged 18 to 85 years who had undergone previous trabeculectomy and/or cataract extraction with intraocular lens implantation and uncontrolled glaucoma with intraocular pressure > or =18 mm Hg and < or =40 mm Hg on maximum tolerated medical therapy. INTERVENTIONS: A 350-mm(2) Baerveldt glaucoma implant or trabeculectomy with mitomycin C (MMC). MAIN OUTCOME MEASURES: Surgical complications, reoperation for complications, visual acuity, and cataract progression. RESULTS: Intraoperative complications occurred in seven patients (7%) in the tube group and 10 patients (10%) in the trabeculectomy group (P = .59). Postoperative complications developed in 36 patients (34%) in the tube group and 60 patients (57%) in the trabeculectomy group during the first year of follow-up (P = .001). Surgical complications were associated with reoperation and/or loss of > or =2 lines of Snellen visual acuity in 18 patients (17%) in the tube group and 28 patients (27%) in the trabeculectomy group (P = .12). CONCLUSIONS: There were a large number of surgical complications during the first year of follow-up in the study, but most were self-limited. The incidence of postoperative complications was higher after trabeculectomy with MMC than nonvalved tube shunt surgery. Serious complications resulting in reoperation and/or vision loss occurred with similar frequency with both surgical procedures.