An apparatus and method for stabilization of aneurysm is disclosed. The apparatus comprises an ultraviolet radiation generator for generating UV radiation having a wavelength, strongly absorbed by the DNA and a catheter including means for delivering the ultraviolet radiation to the aneurysm. The distal end of the catheter is placed inside the aneurysm. Stabilization of the aneurysm is achieved by forming a mural arterial thrombus inside the aneurysm. To make irradiation possible, the blood is displaced from the aneurysm by a steady stream of UV radiation transparent fluid. The injury to the endothelium that triggers the thrombus formation is caused by UV radiation delivered to the aneurysm. In several days after intervention the thrombus becomes fully organized, leaving on the inside surface of the aneurysm a thick layer of fibrotic tissue that stabilizes the aneurysm.