During recent years the increased survival rate of very low birthweight infants has lead to an increased incidence of rickets and/or osteopenia in these infants. The pathogenesis is multifactorial. From several studies performed under different conditions it can be concluded that the vitamin D requirement of these infants is about 3 times higher than the normal prophylactic dose. Breastfed infants should be supplemented with extra phosphorus and possibly also extra calcium. Infant formulas designed for low birthweight infants should have a calcium content compensating for the initially poor calcium absorption of these infants.