Abstract. The majority of bone mineralization occurs during the third trimester of pregnancy and preterm infants are likely to have depleted stores. This puts them at greater risk of fractures. Heparin has been shown to cause osteopenia in adults though fractures are uncommon. There are no data that suggest an association between heparin and fractures in preterm neonates. This report presents the case of a preterm infant who was treated with unfractionated heparin for 3 weeks for an arterial thrombus. Post heparin X-rays demonstrated multiple fractures which did not exist prior to therapy. The temporal association between heparin therapy and fractures suggests that the combination of dose and duration of therapy is a potential risk factor. In preterm infants with already depleted bone mineral content, this could be an important therapeutic consideration.