Objective: To evaluate recurrence and early postoperative complications (sepsis) following surgical excision combined with radiotherapy for troublesome hip heterotopic ossification in patients with spinal cord injury and traumatic brain injury. Design: Retrospective case-control study. Setting: Data relating to patients with spinal cord injury or traumatic brain injury who underwent surgical excision of hip heterotopic ossification were retrieved from the BANKHO database. Case patients underwent excision + radiotherapy, and controls underwent excision only. Control patients were matched to case patients according to sex and age (± 4 years). Participants: Data from 19 case patients and 76 controls were analysed. Main outcome measure: The primary end-point was recurrence of heterotopic ossification. Secondary endpoints were postoperative complications and, more specifically, sepsis that required surgical revision. Results: There was no difference between the odds ratios (OR) for recurrence for each group (OR case group = 0.63, OR spinal cord injury subgroup = 0.45 and OR head injury subgroup = 1.04). The rate of sepsis requiring surgical revision was significantly higher in the case group (p < 0.05). Conclusion: Based on the results of this case-control study, we suggest that radiotherapy should not be combined with surgery in patients with troublesome hip heterotopic ossification undergoing excision. Radiotherapy does not appear to prevent recurrence and, moreover, it is associated with an increased risk of postoperative sepsis.