The potential complications of cataract surgery in the general population are well known. In addition, cataract extraction in the patient with diabetes mellitus is associated with other potential complications common to this disease: neovascular glaucoma and acceleration of proliferative diabetic retinopathy with or without vitreous hemorrhage. We analyzed the records of 154 patients with diabetes mellitus who had undergone standard intracapsular cataract extraction in one eye only with the other eye serving as the unoperated control eye. We were able to determine the status of the diabetic retinopathy before the operation and to note the development of vitreous hemorrhage and rubeosis iridis/neovascular glaucoma after the operation. If either event occurred within six weeks of the surgery, it was considered to be a complication of the cataract extraction. Intracapsular cataract extraction in this diabetic population, without regard of the preoperative status of the retinopathy, was associated with a statistically significant incidence of postoperative rubeosis iridis/neovascular glaucoma (7.8% vs 0%). In patients with preoperative active proliferative diabetic retinopathy, the risk of developing postoperative rubeosis iridis/neovascular glaucoma was even higher (40% vs 0%). There was also a statistically significant incidence of vitreous hemorrhage after surgery in eyes with no diabetic retinopathy or background diabetic retinopathy (6.5% vs 0%). In patients with active proliferative diabetic retinopathy, there was an increased incidence of vitreous hemorrhage after surgery (20% vs 6.5%), but this was not statistically significant due to the small number of patients studied. Possible explanations for these findings are explored and therapeutic and prophylactic measures recommended.