This article reports a case of Kawasaki disease (KD) and its rapid fatal course in a 5-year-old boy, who 3 days before hospitalization demonstrated fever and diffuse erythema in the face, neck, and torso, as well as swelling and pain below the right earlobe. During the admission, he was diagnosed with mumps and suspected scarlet fever. Abnormal laboratory findings included elevated values of procalcitonin, C-reactive protein, and interleukin 6. Sudden death occurred 8 days after admission. Autopsy confirmed the cause of death to be pericardial tamponade due to a ruptured, inflamed aneurysm of the left anterior descending coronary artery. We believe that any typical clinical sign of KD whenever associated with elevated indices of inflammation should set off suspicion of KD and further permit cardiovascular examination. This would contribute to distinguishing KD from other diseases with similar clinical signs in order to accelerate appropriate treatment.