A clinical trial has been conducted to evaluate the effect on vision of laser treatment (argon green or krypton red lasers, assigned randomly) compared with no treatment of eyes with subfoveal choroidal neovascularization associated with age-related macular degeneration. Three months after enrollment, the visual acuity of 37 (20%) of 184 laser-treated eyes had decreased 6 or more lines from the baseline level, while only 19 (11%) of 178 untreated eyes had suffered such large decreases (P = .01, chi 2 test). However, 24 months after enrollment, the visual acuity of only 23 (20%) of 114 laser-treated eyes had decreased by 6 or more lines from baseline compared with 41 (37%) of 112 untreated eyes (P less than .01, chi 2 test). On average, after 24 months, visual acuity of laser-treated eyes had decreased 3 lines from baseline, and visual acuity of untreated eyes had decreased 4 lines (P = .003, t test). Laser-treated eyes retained contrast threshold for large letters at or near baseline levels through 36 months of follow-up examinations, while the contrast threshold of untreated eyes worsened. Persistent or recurrent neovascularization was observed in 51% of the laser-treated eyes by 24 months after initial treatment but was not associated with decreased visual acuity. None of the findings suggested a reason to favor either the argon green or krypton red wavelength. Laser treatment of subfoveal neovascular lesions that meet the eligibility criteria for this study is recommended if both the patient and the ophthalmologist are prepared for a large decrease in visual acuity immediately after treatment.