PURPOSE: The purpose of this study is to examine the usefulness of the head-up tilt test for diagnosis of unexplained syncope in children. METHODS: Head-up tilt test results and clinical features of 41 children with unexplained syncope, presyncope, dizziness and seizure were studied from January, 1997 through January, 2001 at Asan Medical Center. Medical records of children were reviewed retrospectively. The children were evaluated with an 80 degrees head-up tilt test for 15 minutes with or without intravenous infusion of isoproterenol(0.05-0.1 ng/kg/min). RESULTS: 41 children made up the study population, of whom 23(56%) had a positive head-up tilt test and 21(60%) of 35 patients with a history of syncope or presyncope had a positive head-up tilt test. Isoproterenol infusion provoked the more positive head-up tilt test. The patients with positive test results showed three patterns of response to tilting. 16 patients had a predominantly vasodepressor response; three patients had a cardioinhibitory response; and four patients had a mixed response. The patients had an average of five studies performed per patient, including chest radiograph, electrocardiogram, 24 hour Holter monitoring, treadmil test, head computed tomographic scan or magnetic resonance imaging, and echocardiography. The head-up tilt test was most effective for evaluation of unexplained syncope in children. CONCLUSION: Head-up tilt testing performed early in the evaluation will increase the probability of a diagnosis, and will often prevent the need for further extensive, expensive, anxiety-producing tests in children. More controlled studies and a standardization of degree and duration of tilting are necessary to validate the head-up tilt test as a useful diagnostic tool in children with unexplained syncope.