BACKGROUND: To describe the changes in retinal vascular calibre in response to intravitreal ranibizumab injections in patients with neovascular age-related macular degeneration. DESIGN: Prospective interventional case series. PARTICIPANTS: Treatment naïve patients with neovascular age-related macular degeneration were recruited over a 1-year period. METHODS: Each patient received three monthly intravitreal injections according to a 'loading dose'. Retinal arteriolar and venular calibre was measured from digital fundus photographs and summarized as central retinal artery equivalent and central retinal vein equivalent at baseline and 3 months. MAIN OUTCOME MEASURE: Central retinal artery equivalent and central retinal vein equivalent changes from baseline to 3 months. RESULTS: Seventy-four eyes of 71 patients had good quality images for grading vessel calibre at baseline and at 3 months in treated (study) eyes and 51 eyes of 51 patients had good quality images in fellow (control) eyes. Over 3 months, in study eyes treated with ranibizumab, there was a significant increase in central retinal vein equivalent over baseline (+6.20 µm, P = 0.005), but no significant change in central retinal artery equivalent (+0.86 µm, P = 0.55). In control eyes, there was no change in central retinal vein equivalent (-0.82 µm, P = 0.70) or central retinal artery equivalent (0.34 µm, P = 0.75). CONCLUSION: Intravitreal ranibizumab has a significant vasodilational effect on retinal venular calibre in eyes treated for neovascular age-related macular degeneration. The reason for this change is unclear, but may relate to changes in blood flow or inflammatory changes within the retina.