Introduction. As the clinical manifestation of neonatal infection is nonspecific and characterised by varied clinical features, it is highly problematic to establish an early diagnosis. Recently, hopes have been raised by the new acute-phase protein—pentraxin 3 (PTX3). PTX3 belongs to the family of long pentraxins, which is synthesized in numerous cells like endothelial cells, macrophages, and monocytes infiltrating sites of inflammation. Material and Methods. In our research, we have enrolled 29 newborns with infection as the study group and 47 healthy ones as the control group, as well as their mothers. The C-reactive protein (CRP), procalcitonin (PCT), and PTX3 levels were determined in venous blood samples from all investigated neonates and their mothers. Moreover, PTX3 concentrations were assessed in the umbilical cord. Results. There were statistically significant differences in PTX3 levels between healthy and sick newborns both in the umbilical cord (
p
=
0.02
) and venous blood (
p
=
0.01
). The highest PTX3 concentrations were observed in children with infection in the presence of premature rupture of membranes (PROM). PTX3 concentrations in this group were significantly higher compared to those in healthy children without PROM. We observed elevated PCT levels in newborns with infection. No differences in CRP levels in 12 hours of life were noticed between the investigated groups. A comparison of ROC curves for PTX3 and PCT concentrations revealed similar sensitivity and specificity in the prediction of infection in neonates. Conclusions. Serum PTX3 is an important and specific biomarker of early infection. It is already elevated in the umbilical cord, so measuring PTX3 concentration might be useful in the early prediction of infection in newborns.