The objective of this prospective study was to ascertain whether scatter argon laser photocoagulation to the involved sector in major branch retinal vein occlusion and ischemic hemicentral retinal vein occlusion (a) prevents development of retinal and/or optic disk neovascularization and vitreous hemorrhage, and (b) affects visual acuity, visual fields and macular retinal lesions. The study was done in 271 eyes allocated to either treated (n = 61 eyes) or untreated (n = 210) groups. In this study, on an average follow-up of 3.6 years, the laser treatment (1) significantly reduced the risk of development of retinal neovascularization and vitreous hemorrhage, (2) did not affect the visual acuity and macular retinal lesions, and (3) produced a significant worsening in the peripheral visual fields compared to the untreated eyes. In view of our findings, we recommend that argon laser photocoagulation treatment should be given only when neovascularization is seen and not otherwise, because in the latter case, its detrimental effects may outweigh its beneficial ones.