Two cases of leakage of an aortic dissecting aneurysm into the pericardial cavity presenting as acute pericarditis are reported. In both cases the existence of risk factors (hypertension and coarctation of the aorta) suggested the correct diagnosis. Echocardiography showed enlargement of the ascending aorta and thickening of vascular wall in the two cases, furthermore it suggested the presence of aortic insufficiency in one case. The definite diagnosis was made by means of aortography. One patient died after surgery, while the other was successfully treated with hypotensive drugs. Dissecting aneurysm of the aorta may present atypical clinical manifestations; in these circumstances a great suspicion index is the basis for a correct diagnosis. The importance of an early diagnosis by means of aortography and echocardiography is emphasized.