It is a pleasure to share some of our experiences at the University of Pennsylvania regarding head-injured patients and heterotopic ossification (HO).I am not an expert of HO, but through the efforts of people with whom I work closely, particularly Dr Rogers and Gem Spielman, RN, our head-injury clinical co-ordinator, I've learned a lot about HO in recent years.I believe that we neurosurgeons have underappreciated both the frequency and the severity of heterotopic ossification in patients with head injuries. In such patients we're often mainly concerned with intracranial pressure, cerebral blood flow and the CT scan, and with trying to pull the patient through a catastrophic illness.But some of the treatment regimens for head injury have been significantly improved, and we're now better able to control intracranial pressure and cerebral blood flow and other factors. More patients are surviving-but often they're surviving with complications that are potentially preventable, such as HO.So there are two messages I'd like to share with you: One is about which patients in the head-injury population are at high risk for HO, and the other is about the regimen that we've used for HO prophylaxis.We have to keep in mind that nothing in clinical medicine is 100%. The method I'll describe will not prevent HO in every patient. But from preliminary results of some studies we've been engaged in, we think that it's important to begin prevention extremely early-if possible, on the very day of injury-with a prophylactic programme aimed at minimizing and mitigating the occurrence of ossification.