Purpose: This study aimed to determine the optimal initial vancomycin dose to achieve appropriate trough levels in pediatric patients. Methods: We analyzed clinical data for 309 children treated with intravenous vancomycin between 2004 and 2009 at 2 different hospitals in South Korea. The patients were 1-16 years old and exhibited normal renal function. Patient data, including reason for treatment and initial dosing regimen, were reviewed. Two subgroups were identified and compared according to initial vancomycin dose: 40 (35-45) mg/kg/day and 60 (55-65) mg/kg/day. Trough levels were obtained at steady state after at least 4 doses of vancomycin. Results: Patients who received vancomycin had post-operation or wound-related infections (37.2%), localized infection (12.9%), catheter-related infections (9.4%), meningitis (8.7%), or endocarditis (6.8%). Pathogens were confirmed in 79 cases: 28 cases of methicillin-resistant $Staphylococcus$ $epidermidis$ (35.4%) and 25 of methicillin-resistant $Staphylococcus$ $aureus$ (31.6%). Out of the 309 patients, 201 (65%) received vancomycin at 40 mg/kg/day and 108 (35%) at 60 mg/kg/day. Average trough concentrations were significantly different between the groups ($P$<0.001). Trough levels over 10 mg/L were less likely to be achieved in the 40 mg/kg/day group (14%) than in the 60 mg/kg/day group (49%) ($P$<0.001). There were no differences in renal function deterioration between the groups. Conclusion: A common vancomycin dosing regimen, 40 mg/kg/day, was not high enough to achieve trough levels of over 10 mg/L in pediatric patients. Careful drug monitoring must be performed, and increasing initial dose of vancomycin should be considered in pediatric patients.