We retrospectively investigated the effect of warfarin therapy in improving the clinical outcome of Kawasaki disease (KD) patients with giant coronary aneurysms (GAs). We followed 2350 KD patients from 1973 to 2004. The GAs (> or =8 mm in diameter) were diagnosed by coronary angiography. Sixty-eight patients (54 males and 14 females) were retrospectively studied. Patients were divided into two groups. One group consisted of 19 patients with 33 branches treated with a combination of low-dose aspirin and warfarin (target international normalized ratio: 1.5 - 2.5 IU). The second group consisted of 49 patients with 102 branches treated with low-dose aspirin without warfarin. The incidence of myocardial infarction was significantly less in the combination therapy group than in patients treated with aspirin without warfarin (1 patient vs. 16 patients, p < 0.05). Sudden death occurred in seven patients taking aspirin without warfarin, but none of the patients receiving warfarin died. No major bleeding events occurred in either group. Combination therapy of warfarin with aspirin is associated with a decreased risk of myocardial infarction in KD patients with GAs.