The incidence of progression of diabetic retinopathy during pregnancy is unknown and its proper management uncertain. In this study, 55 insulin-dependent diabetic patients under strict glucose control were followed throughout pregnancy with serial retinal examinations by ophthalmoscopy and photographs. Nineteen patients had minimal or background retinopathy and 7 had untreated proliferative changes. Six patients had been treated before pregnancy with photocoagulation for proliferative retinopathy. A positive correlation was found between progressive proliferative diabetic retinopathy and the duration of diabetes mellitus independent of glucose control. During gestation 3 of 19 patients (16%) with minimal or background retinopathy and 6 of 7 patients (86%) with untreated proliferative retinopathy experienced deterioration of their eye disease. In 4 patients with proliferative retinopathy, progression of retinal disease was arrested with photocoagulation during pregnancy. Only 1 of 6 who had received laser treatment prior to pregnancy experienced progression of her retinopathy. These results suggest that photocoagulation prior to pregnancy may protect against rapidly progressive proliferative retinopathy and that aggressive treatment during pregnancy can prevent progression of proliferative retinopathy and visual impairment.