Heterotopic ossification (HO) is a rare complication following total knee arthroplasty (TKA). In the case report presented, a 52-year-old man who had previously undergone TKA for osteoarthritis noticed painful limitation of range of motion (ROM) in spite of active participation in physical therapy and the use of a continuous passive motion machine. A plain radiograph 1 month after surgery revealed HO anterior to the distal femoral shaft in the quadriceps expansion. Ambulation for this patient was limited to short distances because of severe pain and limitation in ROM. The patient underwent manipulation under general anesthesia 2 months after the TKA. Range of motion in flexion improved from 50 degrees to 110 degrees, and the patient became ambulatory without assistive devices. However, the flexion range deteriorated to 50 degrees over a period of 4 months, and ambulation again became significantly limited. The patient underwent resection of HO 6 months after manipulation and regained his ROM to 110 degrees in flexion. He was prescribed indomethacin after surgery for 2 months to prevent recurrence of HO. Follow-up radiographs 3 months after surgery revealed minimal recurrence of HO. The patient's ROM did not deteriorate, and he remained ambulatory. Heterotopic ossification should be suspected in post-TKA patients if ROM does not improve. Physical therapy including ROM exercises remains an essential component in the treatment of HO. Manipulation under general anesthesia or surgical resection of HO may be inevitable in certain patients whose ambulation is significantly limited.