Congenital adrenal cortical hyperplasia (CAH) is one of the commonest endocrine pathologies in the children. Screening newborn infants for CAH is currently based on the measurement of 17-hydroxyprogesterone (17-OHP) levels in blood spots using the immunoenzymatic assay. However, this techniques is known to suffer relatively low specificity accounting for the high percentage of false-positive results. We compared two 17-OHP measurement tecniques, immunoenzymatic assay and liquid chromatography-tandem mass spectrometry (LC-MS/MS) employed for the additional examination of the children in whom screening for CAH revealed the enhanced blood 17-OHP levels. The study included 50 patients at the age from 7 days to 1.5 months born at different gestational ages. 17-OHP levels were measured in all of them using the immunoenzymatic assay and LC-MS/MS. The results of the study indicate that the latter technique should be regarded as the method of choice for the confirmation of diagnosis of CAH. The absence of clinical manifestations of 21-hydroxylase deficiency in the patients in whom the immunoenzymatic assay reveals the enhanced levels of 17-OHP whereas the LC-MS/MS method demonstrates the normal or only slightly elevated concentrations of 17-OHP allows to exclude diagnosis of CAH. The gestational age of the infant is the key factor in the choice of the upper threshold level of 17-OHP for the purpose of screening; the child's body weight is of low diagnostic value. The 17-OHP levels measured by LC-MS/MS in the boys may be slightly higher than the reference values compared with the girls.