The aim of this study is to elucidate the association of neovascularization in branch retinal vein occlusion (BRVO) combined with major arterial insufficiency (MAI), compared with BRVO alone. The authors retrospectively reviewed the charts, color photographs, and fluorescein angiograms of 304 patients (308 eyes) who had BRVO from 1990 to 2002 at Hanyang University hospital. Patients with BRVO combined with MAI and patients with BRVO alone were differentiated by angiographic appearance. Of the 308 eyes, 12 (3.9%) had neovascularization, all of which were in the 56 eyes of the MAI group for which the neovascularization rate was 21.4%. Neovascularization in BRVO was more strongly associated with the non-perfusion caused by MAI, rather than with the extent of the non-perfusion area that originated from retinal capillary obstruction. MAI is considered as a risk factor for neovascularization and hence could be a prognostic factor.