Abstract. BACKGROUND: Vancomycin a frequently used antimicrobial for the treatment of late-onset neonatal sepsis. It can be infused either intermittently or continuously, however, there is no consensus on the optimal dosing regimen. AIM: To evaluate microbiological outcomes, clinical response and adverse events of vancomycin when administered via continuos intravenous infusion. METHODS: The files of preterm infants (<34 weeks), who received either intermittent (group I, n = 41) or continuous (group II, n = 36) vancomycin infusion for the treatment of late-onset sepsis, were investigated retrospectively. Clinical and demographic features were recorded. RESULTS: Clinical improvement rates, Töllner scores and microbiological outcomes did not differ significantly between groups. At 48th hour of vancomycin infusion, 52.8% of infants achieved therapeutic concentrations of vancomycin in group II compared with 34.1% of patients in group I (p = 0.002). Thirty-nine percent of infants in group I had supratherapeutic concentrations of vancomycin at 48th hour compared with 5.6% in group II (p = 0.002). Dose adjustment rate in group I did not differ than group II (65.9% vs. 52.8% respectively, p = 0.3). However, when we subdivide group I into two according to dosing intervals, dose adjustment rates were more common in infants with a gestational age <29 weeks for whom intermittent infusion was performed in 18 hours intervals (92.9% vs 51.9% , p = 0.014). CONCLUSION: In preterm infants, continuous and intermittent infusions of vancomycin have similar clinical efficacies. Continuous infusion is well-tolerated and require less blood sampling compared to intermittent infusion especially in infants less than 29 weeks of gestational age.