Segmental arterial mediolysis (SAM) is a rare disease of unknown aetiology. We report the fourteenth case of SAM, but the first to demonstrate serial changes on arteriography. A 65-year-old woman with abdominal pain underwent laparotomy with resection of an abnormally beaded and narrowed segment of the right branch of the middle colic artery. Characteristic pathological findings of lysis of the arterial media with dissecting haematomas were present. Other than some post-prandial pain, the patient's post-operative course was uneventful. Serial arteriography showed various abnormalities in the trunk and branches of the superior mesenteric artery. Changes in the vessels consisted of three phases, i.e. dilatation, beading with narrowing and restoration of the smooth wall, with various modifications such as aneurysmal enlargement and occlusion.