Therapy programs during the development of heterotopic ossification in spinal cord injury range widely from complete rest to aggressive exercise programs. The literature is confusing by its multiplicity of recommendations because the basic etiology and pathophysiology are unknown and because some basic differences exist between traumatic myositis ossificans and heterotopic ossification associated with severe neurological impairments. Prospective heterotopic ossification roentgenographic (x-ray) surveys of the hips, knees, shoulders, and elbows were made on 250 consecutive spinal cord-injured patients. Those who had x-ray evidence of early or immature heterotopic ossification or who developed early clinical signs of possible heterotopic ossification were treated with an aggressive program of passive progressive range of motion exercises. Several patients who developed bilateral heterotopic ossification had one side used as their own control. Follow-up x-ray studies and range of motion evaluation suggest that an aggressive range of motion exercise program is indicated for patients who are developing or have heterotopic ossification. There is no evidence that exercise increases inflammation with subsequent ossification, and it frequently causes a pseudarthrosis, permitting adequate functional range of motion.