A 76-year-old man was referred to our hospital because of right hydronephrosis. A retrograde pyelogram showed obstruction of the right ureter at the level where it was crossed by the common iliac artery. A computerized tomography scan demonstrated an encased right ureter and aneurysm of right common iliac artery. Arteriography revealed aneurysm of right common iliac artery. An aorto-iliac graft bypass and ureterolysis were performed with intra-peritoneal displacement of the right ureter. The diagnostic procedures and treatment modalities for ureteral obstruction caused by aneurysm are discussed.