A major cause of superficial venous insufficiency is valvular dysfunction in the great saphenous vein. Dilation of the annulus inhibits valve closure preventing reflux in the vein. This study suggests curing dilation by shrinking the collagen fibers in the vein wall using high-intensity focused ultrasound. An in vitro feasibility study was carried out on 20 segments of human saphenous vein. A spherical probe was used to create two 9-mm-long exposure regions on the vein wall in each segment. The focal point of the sound field was moved mechanically along the vein. Different combinations of in situ acoustic intensity and sound source speeds were tested. A contraction index, which expresses the retraction of the vein after ultrasound exposure, was measured between 7 (+/-1) and 24 (+/-8)%. Histologic analysis verified the absence of vein rupture, vein perforation and tissue carbonisation after ultrasound exposure.