One hundred seventy-nine eyes were analyzed to determine the incidence of postoperative complications after vitrectomy for proliferative diabetic retinopathy. One hundred twenty-nine (72%) of the 179 eyes achieved improved vision, and 117 (65%) were considered visual successes with final vision in the functional range of 5/200 or better. Corneal epithelial defects occurred in 51 eyes (28%), but severe corneal complications were rare, and no eye developed corneal clouding as the sole cause of later visual loss. The lens was retained in 128 eyes (75%), and visually significant lens opacities occurred later in 17% of the phakic eyes. Postoperative iris neovascularization was reduced by not removing the lens, and rubeosis iridis occurred in 15 (13%) of 114 phakic eyes and in 21 (32%) of 65 aphakic eyes (P = 0.012). Vitreous hemorrhage was present in 75% of eyes immediately after surgery and cleared in an average of 6.2 weeks in phakic eyes and 5.4 weeks in aphakic eyes. Fifty-two eyes (29%) had recurrent vitreous hemorrhage after the initial postoperative period. New retinal detachment occurred after surgery in 16% of eyes and was treated successfully in 38%. Reoperations were done in 45 eyes (25%), and 32 (71%) of these were for repair of retinal detachment or removal of nonclearing vitreous hemorrhage. Six eyes (3%) developed phthisis bulbi, and one other eye was enucleated.