AIMS/BACKGROUND: Increased retinopathy progression has been reported after cataract surgery in patients with diabetes mellitus. To assess the influence of cataract surgery on visual acuity and retinopathy progression, all diabetic patients who were subjected to cataract surgery during 1991-3 have been followed up at the Department of Ophthalmology in Helsingborg. The average follow up time was 2 years. METHODS: One eye of each of 70 patients was included in the study, 35 monocularly and 35 binocularly operated on. Sixteen of the 70 patients had proliferative diabetic retinopathy (PDR) at baseline. The Wisconsin scale was used for the grading of retinopathy. The degree of glycaemic control was assessed by measurements of HbA1c. RESULTS: Most patients obtained improved visual acuity; a postoperative visual acuity of 0.5 or better was achieved in 89% of diabetic surgical eyes. Progression of the retinopathy occurred in 30 out of the 70 eyes, and was associated with mean level of HbA1c (p = 0.04), duration of diabetes (p = 0.02), insulin treatment (p = 0.001), and presence of retinopathy at baseline (p = 0.01). Patients who progressed had a significantly higher incidence of macular oedema (p = 0.006) than those who did not progress. No significant differences were found when operated and non-operated eyes were compared in the 35 patients with monocular surgery. Two patients in this group, however, ended up with macular oedema and worse vision in the operated eye than in the eye which was not operated on. Both patients had background retinopathy before surgery. CONCLUSIONS: Patients in this study, also those with PDR, obtained good visual acuity, better than in most previous studies. Poor glycaemic control was a factor of importance for the progression of diabetic retinopathy after cataract surgery.