Two neonates with complex cyanotic congenital heart disease, receiving long-term prostaglandin E1 infusion, for 59 and 78 days respectively, demonstrated significant radiographic changes of symmetric cortical hyperostosis of the long bones. Bone biopsies from one of the patients elucidated the histological changes and serial X-rays revealed regression of the hyperostosis. Long-term follow-up after 13 months did not reveal any late bony changes or growth disturbance.