In a double-blind randomized controlled clinical trial conducted in two French and two United Kingdom centers, the effect of antiplatelet agents, i.e., aspirin alone (330 mg 3 times daily) or in combination with dipyridamole (75 mg 3 times daily), was tested versus placebo in 475 patients with early diabetic retinopathy. The assessment of retinopathy was based on change in the number of microaneurysms (MAs) present in the macular field, as seen on fluorescein angiograms, over 3 yr. Forty-one patients did not complete the study. At least three readable initial and yearly angiograms were available on 420 patients (266 treated with insulin and 154 not treated); the results reported are based on these patients. The mean yearly increase in definite MAs was similar in insulin-treated and non-insulin-treated diabetic patients. There was no significant difference between the aspirin-alone group (0.69 ± 5.1 mean ± SD, n = 145) and the aspirin-plus-dipyridamole group (0.34 ± 3.0, n = 142). In the placebo group the mean yearly increase (1.44 ± 4.5, n = 133) was significantly higher than in the treated group (P = .02,1-tailed t test). There was a clear relationship between the deterioration in ophthalmological signs and the increase in mean yearly MAs (clinically stable, 0.38 ± 3.96, n = 293; deteriorating, 1.79 ±4.89, n = 127; P = .002, 2-tailed f test). We conclude that aspirin alone and in conjunction with dipyridamole significantly slows the progression of MA evolution in early diabetic retinopathy.