The Diabetic Retinopathy Study (DRS) demonstrated that prompt argon laser photocoagulation, in comparison to indefinite delay in treatment, could reduce by more than 50% the risk of severe visual loss from proliferative diabetic retinopathy. The DRS also enlightened two generations of ophthalmologists about the value of the randomized controlled clinical trial as a way of assessing new and existing treatments for unsolved therapeutic problems. After the example of the DRS, laser treatment was shown to be effective in reducing vision loss in selected patients with branch retinal vein occlusion, age-related macular degeneration, ocular histoplasmosis, and diabetic macular edema. Existing trials, supported by the National Eye Institute, are seeking to determine the appropriate treatment for selected patients with newly diagnosed glaucoma, vascularized corneas, retinopathy of prematurity, proliferative vitreoretinopathy and complicated retinal detachment, and choroidal melanoma. Clinical practice has benefited enormously from these studies all of which owe their existence, at least in part, to the prototypical clinical trial, the DRS. This symposium discusses the DRS and places it in today's perspective, with a look to the past as well.