AbstractReduction of vascular recoil is an important goal of laser balloon angioplasty (LBA), wherein Nd:YAG laser radiation is delivered radially during balloon inflation. To define the acute and chronic effects of LBA on the normal arterial lumen in comparison with those of balloon angioplasty (BA), 36 New Zealand White male rabbits (3–4 kg) were subjected to LBA of an external iliac artery and to BA of the contralateral artery with two 1‐minute balloon inflations. During LBA, which was performed during the second balloon inflation, either 300 (n = 26) or 176 (n = 10) J were delivered to achieve high and moderate laser doses, respectively, in different LBA groups. Angiography was performed pre‐ and post‐LBA/BA and subsequently at intervals of either 1, 2, 7, 28, 48, or 223 days. Automated analysis of digitized images was used to measure lumen diameter. No instance of perforation or thrombosis occurred. LBA‐treated arteries acutely showed an increase in mean diameter over baseline (+.5 mm, P<.01) and that of BA‐treated arteries (+.4 mm, P<.01). While arteries treated with the high laser dose showed a loss of the initial gain in lumen diameter by 1 month, caused by both extravascular fibrosis of the thin‐walled (<0.1 mm) artery and mild neointimal proliferation which were not reduced by daily administration of aspirin in seven rabbits, arteries treated with the moderate laser dose retained the increment in mean diameter at 1 month over that of BA‐treated arteries (+.5 mm, P<.05). Thus, unlike BA, LBA increases luminal diameter acutely and, at a moderate laser dose, chronically.