Pars plana vitrectomy was used to treat 134 consecutive eyes with complications resulting from proliferative diabetic retinopathy, including nonabsorbing vitreous hemorrhage, recent traction and rhegmatogenous retinal detachment, progressive fibrovascular proliferation, and early rubeosis iridis with recent vitreous hemorrhage. Vision improved after surgery in 65% of the eyes, was unchanged in 16%, and decreased after surgery in 19%. In 24% of the successful cases, vision of 20/50 or better was achieved. When all posterior cortical vitreous was removed, no preretinal fibrovascular growth occurred after surgery. Nonatrophic epiretinal fibrovascular membranes that were not removed usually underwent centripetal contraction after surgery, causing tangential traction on the adjacent retina. Rubeosis iridis was the most common postoperative complication in otherwise successful cases, and rubeosis underwent regression after scatter retinal photocoagulation in some eyes.