We report the case of a 3 yrs old boy with the most serious complication of Kawasaki disease. 2 dimensional echocardiography detected multiple coronary aneurysms and in the giant left coronary aneurysm a thrombus formation. The thrombus disappeared after one week anticoagulant therapy. In addition the aneurysm were proved by coronarography. During the 2 years follow-up period the child is on anticoagulant therapy and he is symptom free. This is the first case in our country with a huge thrombus in a giant coronary aneurysm due to Kawasaki disease who was successfully treated using anticoagulant therapy.