Bioavailability can be broadly defined as the absorption and utilization of a nutrient, both of which may be affected by such host factors as gender, physiologic state and coexisting pathologic conditions. This report highlights factors of particular importance for the bioavailability of nutrients for infants, children and adolescents. Considerations for nutrient bioavailability for pediatric populations include maturation of the gastrointestinal tract, growth, character of the diet, and nutritional status. Critical periods of development include early infancy (0-6 mo), late infancy/early childhood (6-24 mo) and adolescence (12-18 yr). Iron, zinc and calcium are minerals of particular interest and importance to pediatric populations and are susceptible to alterations in bioavailability. In the young infant, iron and zinc are highly bioavailable from human milk. By approximately 6 mo of age, other dietary sources are needed to maintain continued normal status. In breastfed infants who were born prematurely or with low birth weight, earlier supplemental iron is often recommended. For the older infant and toddler, iron and zinc are also important for normal growth and development. The bioavailability of these trace minerals in complementary foods is discussed. During adolescence, adequate calcium intake is critical to normal bone mineralization. In girls, peak calcium absorption and calcium deposition in bones occur at or near menarche, which illustrates the importance of the physiologic state on mineral bioavailability. Investigations into nutrient bioavailability must carefully consider these factors, because the failure to have well-matched comparison groups with respect to age and/or nutritional status may inadvertently mask differences in nutrient utilization.