Objective: To determine the predictive value of serum levels of creatine phosphokinase (CPK) and alkaline phosphatase (ALP) in identifying patients with spinal cord injury (SCI) who are at risk to develop heterotopic ossification (HO) at the hips. Design: Prospective cohort study. Setting: Tertiary-care level I trauma center. Participants: Consecutive sample of 18 adults with acute traumatic SCI. Patients were excluded if they had medical or surgical conditions that are known to cause elevated enzyme levels. Interventions: Not applicable. Main Outcome Measures: Conventional hip radiographs were taken approximately 3 weeks after injury and again from between 3 to 6 months after injury. Serum ALP and CPK were measured approximately 3 weeks after SCI. Patients were later separated into 2 groups: group 1 was comprised of those who developed HO and group 2 was comprised of those who did not. Results: The initial radiographs showed no evidence of HO in either group. The radiographs taken at 3 to 6 months showed HO in 7 of 18 patients. The levels of CPK at the initial evaluation were significantly higher (R=.947, P<.0024) in group 1 than in group 2 and correlated with the severity of HO. There was no correlation between serum ALP levels and subsequent development of HO between the 2 groups (P=.07). Conclusion: Elevated serum levels of CPK have value in predicting the HO.