Aim: Neuropilin 1 (NRP1) and the structurally-related molecule, neuropilin 2 (NRP2), are co-receptors both for class 3 semaphorins, a family of secreted polypeptides with key roles in axonal guidance, and for various members of the VEGF family. Neuropilins were also identified to be key players in other physiological and pathological settings such as the primary immune response and cancer. Our group identified Neuropilins (NRPs) as regulators of vascular smooth muscle cell (VSMC) migration 1. In this study, we explored the role of NRP1 in abnormal VSMC accumulation in vivo in the rat carotid artery model of neointimal hyperplasia following balloon injury, in which VSMC migration and proliferation play important roles. Methods: Male Sprague-Dawley rats were subjected to balloon angioplasty and left to recover for 7, 14 or 28 days. Quantitative PCR and Western blotting were used to look at endogenous levels of NRPs expression in carotid arteries at the different recovery times. At the time of surgery, we applied 30% pluronic gel containing 10E10 adenoviral (Ad) particles expressing control LacZ, NRP1 Wild-Type (WT) or a truncated form, devoid of intracytoplasmic domain (NRP1ΔC), to the adventitia. Morphometric analysis was used to quantify the intima/media ratios in adenovirus-transduced arteries; Western blot and absolute RT-qPCR were used to detect changes in protein expression and mRNA levels respectively. Results: Endogenous NRP1 and NRP2 mRNA and protein levels are upregulated after carotid injury with a maximum protein expression 7 days after injury, expression remaining elevated thereafter. Morphometric analysis of the vessels revealed that the over-expression of NRP1-WT did not alter the extent of neotinima formation but the NRP1ΔC mutant decreased the formation of neointimal hyperplasia. Conclusions: These results strongly suggest a role for NRPs in the development of neointima in the rat carotid artery model of restenosis. Insights into NRP function in the aberrant migration and proliferation of VSMC in this model could be crucial to understand the mechanism of VSMC accumulation occurring in vascular remodeling.