Objectives The aim of this study was to investigate if radiation therapy (RT) favorably modulates wound healing at vein graft anastomoses. Materials and methods Jugular vein grafts were sewn into carotid arteries in 32 rats which were randomly divided into two groups: RT (gamma source, 14 Gray, n=16) and control (C, sham irradiation, n=16). Grafts and adjacent arteries were analyzed at 2 ( n=8) and 8 weeks ( n=8) by histology, immunohistochemistry, and morphometry. Results Although, RT did not reduce the overall occurrence of intimal hyperplasia, the distribution differed. RT led to a reduction of intimal hyperplasia in arterial segments (median: C: 41.873 μm 2; RT: 6.452 μm 2, p<0.0007). In contrast, RT augmented intimal hyperplasia in vein grafts (median: C: 30.287 μm 2; RT: 90.455 μm 2, p<0.014). Vein graft diameters after RT were enlarged (median: C: 2.098 μm; RT: 3.381, p<0.031). Over 80% of the cells were of mesenchymal origin in both groups. Conclusions RT reduced intimal hyperplasia in arterial segments. However, RT led to graft dilatation and increased intimal hyperplasia in vein grafts. RT did not favorably modulate the vascular wound healing response in this model.