In this case report the development of a vitamin K deficiency in a neutropenic adolescent receiving parenteral nutrition following bone marrow transplantation is described. The parenteral nutrition solution did not provide vitamin K and the patient had been receiving oral antibiotics prior to and during use of the intravenous feeding. Oral intake was minimal. Standard adult oral and intravenous multivitamin preparations for use in individuals older than 11 years do not routinely contain this vitamin. The function of vitamin K and causes for development of a deficiency are reviewed. Recommended intakes and guidelines for supplementation are also discussed.