A 52-year-old Japanese man who had suffered from Behçet's disease since the age of 45 years was admitted to hospital for evaluation of syncope and heart murmur. Echocardiography and aortography revealed severe aortic regurgitation and cystic masses under the right coronary cusp and the left ventricular outflow tract, but no shunt jet. He was diagnosed with unruptured aneurysm of the sinus of Valsalva, and surgical closure of the orifice of the aneurysm was performed. The diameter of the orifice was 11 mm and the aneurysm was 15 mm in depth, and consisted of 2 chambers. Because the aortic regurgitation was reduced after patch closure of the orifice, aortic valve replacement was not performed. Unruptured aneurysm of the sinus of Valsalva is a rare clinical lesion, but patients with active inflammatory disease of the aorta, such as in Behçet's disease, should have periodic echocardiography for early detection of an aneurysm or valvular involvement, even if there are not any symptoms.