Conventional interval dosing (CID) and extended interval dosing (EID) of gentamicin were compared in preterm infants. Gentamicin peak and trough levels, serum creatinine, urine output, and hearing screens were obtained in 40 preterm infants. Results suggest that EID is safe, provides gentamicin levels in desirable ranges (peak, 5 to 12 microg/mL; trough < 2 microg/mL), and reduces dosage adjustments.