Of 220 patients (250 eyes) who underwent extracapsular cataract extraction with implantation of a posterior chamber intraocular lens, 36 (45 eyes) with non-insulin-dependent diabetes mellitus had no retinopathy, simple, or preproliferative retinopathy. They were divided into group A patients who underwent diet therapy or were treated with oral agents and group B patients who were given insulin therapy. The 184 patients (205 eyes) without diabetes mellitus served as control (group C). Transient elevation of intraocular pressure and cystoid macular edema were observed more frequently in diabetic patients (groups A and B). Progressive retinopathy occurred more frequently in group B than in group A patients, and it correlated with increased levels of plasma glucose. Unilateral cataract surgery was performed on 27 diabetic patients. Nine (33%) operated eyes showed progressive retinopathy, while one (4%) fellow eye worsened. It is possible that both increased levels of plasma glucose and surgical procedures may participate in the progression of retinopathy.