Procalcitonin (PCT) has been proposed as an interesting marker in the diagnosis, prognosis, and response to treatment of patient with neonatal sepsis. Fifty-nine neonates (34 males and 25 females) with a mean gestational age of approximately 31 weeks and a mean weight of about 1750 g admitted in the Neonatal Intensive Care Unit of Cagliari (Italy) were evaluated in controls and in infected neonates, before and after 48 h of life. From our experience it emerges that PCT is a marker of early and late neonatal sepsis which is reliable in preterm neonates. A cut-off of 0.5 ng/ml starting from the third day of life appears to be capable of ensuring good test sensitivity and specificity.