Objective: To report the design, baseline patient characteristics, and intraoperative complications of the Ahmed Versus Baerveldt (AVB) Study. Design: Multicenter, randomized, clinical trial. Participants: Patients were recruited from 7 international clinical sites and treated by 10 surgeons between 2005 and 2009. Inclusion criteria required that patients be at least 18 years of age and have uncontrolled glaucoma refractory to medicinal, laser, and surgical therapy. Methods: Eligible patients were randomized to undergo implantation of an Ahmed-FP7 valve (New World Medical, Inc., Rancho Cucamonga, CA) or a Baerveldt-350 implant (Abbott Medical Optics, Inc., Santa Ana, CA) using standardized surgical technique, to be followed for 5 years. Main Outcome Measures: The primary outcome measure was failure, defined as intraocular pressure (IOP) out of target range (518 mmHg with <20% reduction from baseline) for 2 consecutive visits after 3 months, vision-threatening complications, additional glaucoma procedures, or loss of light perception. Secondary outcome measures included IOP, medication use, visual acuity, complications, and interventions. Results: A total of 238 patients were enrolled in the study; 124 received the Ahmed-FP7 valve implant and 114 received the Baerveldt-350 implant. The 2 treatment groups did not differ in any baseline characteristics with the exception of sex. The mean age of the study group was 66±16 years, and 55% were women, with a greater proportion in the Baerveldt group (P=0.01). The mean baseline IOP of the study group was 31.4±10.8 on a mean of 3.1±1.0 glaucoma medications. The median Snellen visual acuity was 20/100, mean number of previous laser therapies was 0.9±1.1, and mean number of previous surgeries was 1.7±1.2. Five (4%) patients in the Ahmed group and 4 (4%) patients in the Baerveldt group experienced significant intraoperative complications. Conclusions: Aqueous drainage devices are being increasingly used for glaucoma refractory to conventional treatment, and the AVB Study compares the 2 most commonly implanted devices. The 2 groups had similar baseline characteristics, and there were a similar number of intraoperative complications for both devices. Financial Disclosure(s): Proprietary or commercial disclosure may be found after the references.