Significant benefits to infant host defense, sensory-neural development, gastrointestinal maturation, and some aspects of nutritional status are observed when premature infants are fed their mothers' own milk. A reduction in infection-related morbidity in human milk-fed premature infants has been reported in nearly a dozen descriptive, and a few quasi-randomized, studies in the past 25 years. Studies on neurodevelopmental outcomes have reported significantly positive effects for human milk intake on mental and motor development, intelligence quotient, and visual acuity compared with the feeding of formula. Human milk-fed infants also have decreased rates of re-hospitalization after discharge. It is unclear how much human milk is needed to provide protection or at what postnatal age the protective effects maximize. More data are warranted to elucidate these questions. Despite the significant benefits of mothers' own milk, nutritional adequacy may be a limiting factor in the infant weighing less than 1500 g at birth. The overall nutritional needs of these infants can be supported with a nutrient supplement, or fortifier, added to the milk.