PURPOSE: To examine angiographic risk factors for the recurrence of macular edema associated with branch retinal vein occlusion. METHODS: We consecutively included 51 patients with treatment-naive branch retinal vein occlusion involving the macular area. Each eye initially received 3 monthly ranibizumab injections, with additional injections as necessary. At Month 3, we examined parafoveal vessel diameter indexes (VDI) in all sectors using optical coherence tomography angiography and determined the association with retinal thickness changes (Month 3-Month 5) and the number of ranibizumab injections during 12 months. RESULTS: Parafoveal VDIs in the affected, nasal, and temporal sectors at Month 3 were significantly associated with corresponding parafoveal thickening (P = 0.020, 0.010, and <0.001, respectively), and the parafoveal VDIs in the affected and temporal sectors were significantly associated with future foveal thickening (P = 0.037, and 0.026, respectively). Moreover, the parafoveal VDI in the temporal sector showed a significant association with the total required number of ranibizumab injections (P = 0.040). CONCLUSION: The parafoveal VDI may adequately represent the degree of congestion associated with branch retinal vein occlusion. Particularly, the VDI in the temporal sector may be a good predictor of future retinal thickening in the corresponding parafovea and the fovea and the number of ranibizumab injections.