Fewer than 20 cases of adventitial cystic disease of the vein have been reported in the worldwide literature. This small number of reported cases may be due not only to the disease's low incidence, but also to the difficulty in making the proper diagnosis. Many techniques have been used to investigate this disease, but venography has been the traditional diagnostic tool. In this report we present a case of adventitial cystic disease that was well demonstrated by CT venography.