The authors report a case of false aneurysm of the superior mesenteric artery, complicating acute pancreatitis. They insist on the sonographic signs of "the cyst within a cyst"; the presence of a cystic lesion located within a larger mass an US Scanning is highly suggestive of a false aneurysm included in a pseudocyst. They demonstrate the correlation between US Scanning, CT Scan and arteriogram.