A retrospective study was conducted to determine the incidence of deaths from exertional myopathy (EM) in the hoofstock collection at the National Zoological Park (NZP) from 1975 to 1985. The diagnosis of EM was based on history, clinical signs, clinicopathological findings, gross and microscopic lesions. Only bovids, cervids, and equids were included in the study. Data were derived from the medical and pathological records of the NZP. There were 10 cases of EM during this period, but only seven deaths were directly attributable to EM. Five deaths occurred after immobilization. Two deaths occurred after improper transport, but the anesthetic history was not known in these cases. Pathologic changes consistent with EM were incidental findings in an animal killed by dogs, and in two animals euthanized because of suspected infection with Parelaphostrongylus tenuis. Only cervids and bovids were affected. There was no age or sex predilection for developing EM and deaths occurred throughout the year. Deaths associated with immobilization occurred most often after anesthesia with xylazine and etorphine. These are the drugs used most frequently in bovid and cervid anesthesia at the NZP. The overall incidence of deaths from EM after immobilization was 0.25% for the 10-yr period.