Mucocutaneous lymph node syndrome (Kawasaki's disease) is an acute febrile, exanthomatous illness in which massive lymphadenopathy may occur in the cervical area. This lymphadenopathy may mimic other conditions and present a diagnostic dilemma. We present a case report of a child whose initial clinical signs, symptoms, and laboratory findings were compatible with acute coalescent mastoiditis; however, the child was found after close observation to have Kawasaki's disease. The case demonstrates the similarity between the two diseases and how close observation can prevent unnecessary surgery. When considering the rare diagnosis of mastoiditis, other entities need to be considered in the differential diagnosis before surgical intervention is undertaken. If the patient is unstable or a threatened complication of mastoiditis is apparent, however, immediate mastoidectomy is required.