Iron is essential for brain development and there is a well established association between iron deficiency in infants and poor neurological development. In Sweden, about 5% of newborns have low birth weight (< 2500 g). Due to small iron stores at birth and rapid postnatal growth, they have increased risk of iron deficiency and it is therefore important to prevent iron deficiency in this population. However, excessive iron supplementation can have adverse effects in infants such as growth impairment. In a randomized, controlled trial, we are investigating the effects of 0, 1 or 2 mg/kg/d of iron on brain myelination, cognitive development and growth in low birth weight infants.