There is an increase in the survival rate of preterm infants due to rapid advances in medical knowledge and technology. However, the research and attention paid to the proper use of pharmacotherapy in these infants is still a relatively underdeveloped field. Effective and safe drug therapy requires a thorough understanding of human developmental biology and of the dynamic ontogeny of drug absorption, drug disposition, drug metabolism, and drug excretion. It is apparent that maturation of organ system function and changes in body composition during gestation and during the neonatal period exert a significant effect on the disposition of drugs. This review focuses on the effects of maturational and drug-induced changes in renal function on clinical pharmacokinetics in the preterm infant.