We herein report 3 cases of acute aortic dissection (AAD) in which the initial 12-lead electrocardiogram showed typical ST elevation consistent with acute pericarditis. All patients exhibited small pericardial effusion but did not suffer from rupture into the pericardium or clinical tamponade. Slow leakage or exudate stemming from the dissecting hematoma appeared to have caused inflammation, resulting in pericarditis. Therefore, we highlight the fact that AAD may masquerade as acute pericarditis. Physicians should be aware of the possibility of type A AAD as an important underlying condition, since the early diagnosis and subsequent surgical treatment may save patients' lives.