Extracorporeal membrane oxygenation (ECMO) may affect the pharmacokinetics of certain drugs. The objectives of this study were to determine (1) the pharmacokinetics of gentamicin in neonates on ECMO and compare them to reported values for a similar patient population not on ECMO, (2) if the pharmacokinetics of gentamicin differ between venous-venous and venous-arterial bypass, and (3) if the pharmacokinetics of gentamicin are affected by oxygenator surface area (0.6 m2 vs 0.8 m2 oxygenators). The medical records of 29 term neonates who received gentamicin while on ECMO were reviewed. Data collected included gentamicin dosage, peak and trough serum concentrations determined at steady state, duration of treatment, time on ECMO, daily weights, and pertinent laboratory values. An initial dosage of gentamicin 2.5 mg/kg every 18 hours is suggested for term neonates on ECMO. Dosage adjustments should be based on gentamicin serum concentrations, and modifications may also be required after ECMO.