The aim of this study was to investigate the molecular epidemiology of infections caused by antibiotic resistant Enterobacteriaceae in very-low birth weight neonates. The results have shown that the risk factors for infections caused by E. coli (in relation to infections caused by other pathogens) are low gestational age, low birth weight, low Apgar score, as well as maternal genital tract colonization during pregnancy with E. coli.Additionally, the problem of high mortality in E. coli associated infections (comparing to infections of different etiology) was highlighted and connected with the high resistance and virulence of the pathogen.Furthermore, it has been shown that E. coli did not show clonality. It was different in case of K. pneumoniae, which showed genetic similarity – horizontal transfer of K. pneumoniae strain on one of the wards was detected. Therefore, detailed monitoring of infections caused by K. pneumoniae should be implemented and more effective system of infection control should be introduced. The results indicated also a problem with plasmid-mediated fluoroquinolone resistance, which can be easily transferred to other strains.The results indicate the need for further study of the epidemiology of the infections caused by Enterobacteriaceae in newborns with low birth weight, due to the fact of their increasing participation in the pathogenesis of such infections. Molecular studies are of particular interest, transmission patterns should be studied, as it may help to reduce the number of infections transmitted horizontally. In addition, research on resistance and resistance mechanisms may contribute to the development of new guidelines for empiric therapy of infections in low birth weight infants.