Donor human milk (DHM) is increasingly being used in neonatal intensive care units (NICUs) to achieve exclusive human milk (EHM) feedings in preterm infants. The aim of the study was to determine the cost of DHM to achieve EHM feeding for very preterm infants. The hypothesis was that the cost of DHM per infant is modulated by the availability of mother's own milk (MOM). Preterm infants (<1,500 g at birth weight or <33 weeks in gestational age) were retrospectively evaluated for a 1-year interval. MOM, DHM, and formula feeding categories were determined. A DHM feeding log was retrospectively analyzed for feeding volumes (in milliliters) and duration (in days). Four categories were created, based on maternal ability to provide sufficient breastmilk volumes and her intention to breastfeed. The volume, duration, and cost of DHM were calculated for each category. Forty-six of the 64 (72%) infants admitted to the NICU who were <33 weeks in gestational age received DHM. Four categories of DHM use were observed. The mean costs of DHM were $27 for infants of mothers who provided sufficient breastmilk through to discharge, $154 for infants of mothers who had insufficient milk supply during admission, $281 for infants of mothers who went home on formula but received any volume of MOM during admission, and $590 for infants who received no MOM during admission. Most NICU mothers (72%) of very preterm infants were unable to provide all of the milk necessary for an EHM diet. Few infants (15%) received exclusively DHM. The cost of DHM per NICU infant ranged from $27 to $590 and was influenced by the mother's willingness or ability to provide human milk.