We report a four-month-old boy with incomplete Kawasaki syndrome. He developed a coronary artery aneurysm. Incomplete Kawasaki syndrome is rare in Denmark, and only reported in five patient cases in the past 25 years. It is difficult to diagnose Kawasaki disease; early diagnosis and treatment reduces the risk for cardiac sequel. In lack of diagnostic test, we recommend that the algorithm from the American Heart Association to diagnose incomplete Kawasaki is implemented in Denmark. The algorithm is based on classic clinical features, echocardiography and laboratory findings.