OBJECTIVE: To study the diagnostic value of head up tilt table test in childhood unexplained syncope. METHODS: Thirty children with this disorder aged from 6 to 18 years old (mean 11.74 ± 2.82 ) were taken the 70 degrees head up tilt table test. Blood pressure and electrocardiogram were recorded at 5 minute intervals by multifunctional monitor in these subjects. The result of the test was evaluated according to the symptoms of patients during the test. RESULTS: Of the 30 subjects, 10 presented positive reaction of head up tilt table test ( 33.3% ), in which 5 showed the reaction type of heart inhibition and 5 of blood vessel inhibition. The syncope episodes occurred after standing time of 10 40 min (mean 24.0 ± 12.2 ). CONCLUSIONS: The head up tilt table test may be a useful method in the diagnosis of vasovagal syncope, helping to determine the origin of unexplained syncope in children