During hospitalization in the neonatal intensive care unit (NICU), the brain of the preterm infant undergoes a particularly vulnerable and sensitive period of development. Brain development might be negatively influenced by direct injury as well as by complications of prematurity. Over the past few years, stress has come to be increasingly recognized as a potential risk factor. The NICU environment contains numerous stress factors due to maternal deprivation and over-stimulation, such as light, sound and pain, which conflict with the brain's developmental requirements. Developmental care is a caregiving approach that addresses the early developmental needs of the preterm infant as an integral component of quality neonatal care. NIDCAP (Newborn Individualized Developmental Care and Assessment Program) is a comprehensive program that aims to reduce environmental stress, to support the infant's neuro-behavioral maturation and organization, and to promote early parent-infant relationships. The implementation of developmental care based on NIDCAP principles is a gradual, in-depth systems change process, which affects all aspects of care in the NICU. This review describes the theoretical basis of the NIDCAP approach, summarizes the scientific evidence and addresses some of the implications of the transition from a traditional to a developmental care NICU.