Age-related macular degeneration (AMD) is one of the leading causes of blindness in the world. Most of the severe vision loss associated with AMD is due to the development of choroidal neovascularization (CNV). The specific causes of AMD and in particular, its neovascular phase, remain uncertain. During the past two decades a number of large prospective clinical trials, observational epidemiologic studies, and population- based cohort studies have furthered our understanding of this blinding ocular condition. The Macular Photocoagulation Study has received praise for its many contributions in the laser treatment of neovascular complications of AMD; however, these trials have made other significant contributions by helping to better define the natural history of AMD, and in particular, risk factors for the development of CNV in eyes with non-neovascular disease. This type of information may provide significant clues for researchers regarding disease pathogenesis and identify a high-risk group in whom to target new treatment strategies. For patients currently diagnosed with macular degeneration, this information can lead to a better understanding of their condition and a more accurate prognosis of their ocular health and vision status. This article reviews information from a variety of sources to investigate incidence rates and risk factors for the development of CNV in the fellow eye of patients with AMD and unilateral neovascular maculopathy.