A 2.5-month-old boy admitted to our hospital with irritability, poor feeding and fever of 12 hours duration. On physical examination, he was febrile and extremely irritable. Initial whole blood count revealed a hemoglobin level of 10.1 g/dl, white blood count of 17,800/mm3 and platelet count of 454,000/mm3. Erythrocyte sedimentation rate was 80 mm/h and C-reactive protein was 3.96 mg/dl. Biochemical examinations of serum, urinalysis, chest X-ray, and analysis of cerebrospinal fluid (CSF) were normal. He was started on intravenous ampicillin and ceftriaxone empirically for provisional occult bacteremia. His blood, urine and CSF cultures were negative. On the 7th day of the treatment, there were no additional symptoms or findings other than fever. Echocardiography revealed aneurysms in both the left and right coronary arteries. Intravenous immunoglobulin (IVIG) and per oral aspirin were administered, and the fever resolved after IVIG infusion. Two years later, the echocardiography showed disappearing of the saccular aneurysm on the right coronary artery, but the dilatation of the left coronary artery was persisting. In conclusion, incomplete Kawasaki disease should always be included in the differential diagnosis of an infant with persistent fever, especially one younger than three months of age, when the conventional work-up fails to reveal the underlying cause.