Objective: Sepsis is a life-threatening disease which is associated with high rates of morbidity and mortality. The critically ill patients often manifest a Systemic Inflammatory Response Syndrome (SIRS) which is independent of an infection. The early diagnosis of different severities of sepsis is important for an early implementation of the specific therapies. Our objective was to evaluate the diagnostic and the prognostic values of blood Procalcitonin (PCT) in cases of bacterial septicaemia in children. Methods: The total sample comprised of 150 subjects who were admitted to the ICU with septicaemia and 50 normal, healthy, age and sex matched children. The first sample was collected at the time of admission, before the start of the antibiotic therapy (TO). A second sample was collected at 24 hours (T24) and a final sample was collected at 96 hours (T96). A PCT value of > 0.5ng/m1 was accepted as positive. Results: 63% of the children who were diagnosed with a bacterial aetiology showed detectable blood PCT levels with higher concentrations, while in the children who were diagnosed with a viral aetiology, only 22.2 % had detectable PCT levels, but in lower concentrations. The mean percentage reduction in the PCT value among the bacterial infection subjects was 44.39 +/- 41.82 as compared to that in the viral infection subjects (5.71 +/- 26.68) and in the subjects where the aetiology was not established (5.71 +/- 20.08). Conclusion: The results which were obtained in our study confirmed that the PCT levels were a better marker for the bacterial infections. The PCT measurements may be used as a guide to the antibiotic therapy in critically ill children with suspected sepsis.