OBJECTIVE To estimate an appropriate once-daily gentamicin dose and dosing interval for non-critical care pediatric patients older than 3 months of age without cystic fibrosis. METHODS Pharmacokinetic analysis of data from a retrospective medical record review. METHODS Large academic children's hospital. METHODS One hundred fourteen non-critical care pediatric patients older than 3 months of age without cystic fibrosis who received multiple-daily dosing regimens of gentamicin between September 2007 and April 2008. RESULTS Patient-specific pharmacokinetic parameters were calculated using drug concentrations obtained at steady state. Once-daily doses were extrapolated for each patient to achieve goal peak and trough concentrations. Using the average of these doses and the patient-specific pharmacokinetic parameters, theoretical once-daily peak and trough concentrations were calculated for each patient. Patient characteristics were analyzed to determine differences between patients who did and those who did not achieve adequate peak concentrations. Mean +/- SD pharmacokinetic parameters were as follows: elimination rate constant 0.32 +/- 0.06 hour(-1), half-life 2.28 +/- 0.54 hours, and volume of distribution 0.24 +/- 0.08 L/kg. The only patient demographic characteristic found to have a significant effect on the extrapolated peak concentration was age. The following age-specific once-daily doses were calculated: 3 months to less than 2 years, 9.5 mg/kg; 2 years to less than 8 years, 8.5 mg/kg; and 8-18 years, 7 mg/kg. CONCLUSIONS Age was the primary factor in determining the once-daily dose of gentamicin in our pediatric population. Further prospective research is necessary to determine the safety and efficacy of these age-based, once-daily doses for gentamicin.