The course of diabetic retinopathy following phacoemulsification and in-the-bag implantation of an intraocular lens (IOL) was studied prospectively in 223 patients (223 eyes). A total of 205 eyes were followed for 6 months. The nonoperated fellow eyes served as a control group. At the time of surgery, 158 patients had no diabetic retinopathy, 45 showed untreated background retinopathy, and 20 had more serious retinopathy with previous coagulation therapy. At 6 months of follow-up, 18.4% of the operated eyes without preoperative retinopathy developed background retinopathy, as did 14.3% of the untreated fellow eyes. Worsening of preexisting diabetic retinopathy during the observation period occurred in 27.6% of the operated eyes and in 29.3% of the non-operated eyes. Although the final visual acuity achieved in our patients was poorer than that reported for nondiabetics, our functional results were satisfying: 94.1% of the operated eyes showed improved visual acuity 6 months postoperatively, 2.4% deteriorated, and 3.4% were unchanged. We therefore conclude that cataract surgery in diabetic patients can be performed with an acceptable risk of complications. Furthermore, worsening of diabetic retinopathy seems to be correlated not with the cataract surgery but with the natural course of diabetic vascular disease.