BACKGROUND: Hematocrit (HCT) is significantly higher in newborns than in adults, but this fact is not usually considered when performing coagulation tests in newborns. We studied 71 healthy full-term newborns and compared them to 100 healthy adults to test the hypothesis that correcting the anticoagulant-to-blood ratio for neonatal HCT would reduce the differences among the two populations. METHODS: PT, PTT, fibrinogen, platelets and factors II, VII, IX, X, V, VIII were measured in 71 healthy full-term newborns and 100 healthy adults. An anticoagulant-blood ratio corrected for HCT was used. In 16 newborns, a non corrected value was also used and results were compared with the corrected ratio. RESULTS: A significant difference was observed between newborns and adults in all tests with the exceptions of fibrinogen and factor V. In the 16 newborns from whom blood was collected without correcting in the anticoagulant, a significant difference was also found in all parameters but fibrinogen. A weak correlation linked the different variables. CONCLUSIONS: After correction for HCT, neonatal PT and factors V, VII, VIII and IX were much closer to adult values; neonatal PTT and factors II and X were still definitely lower.