Chronic low back pain is a difficult problem, especially, in patients who had been operated. Characteristically they showed pain behavior and used to refractory to any kind of treatment. Failed Back Surgery Syndrome is a group of disorders with persistent or recurrent symptoms following spinal surgery, with hallmarks of back pain, sciatica, and functional impairment. We investigated 37 chronic low back pain patients who have been operated at least once. They were reviewed medical records and were taken MagnevistⰒ-enhanced magnetic resonance imaging in the postoperative periods. This paper presents the causes of failed back surgery syndrome in the bases of clinical symptoms and MRI findings.

The results were as follows;

1) Among 37 patients, patients who had pain-free-interval less than 6 months were 29 and more than 6 months were 8.

2) In 19 patients who had revealed radiating leg pain, 7 patients were suffered from low back pain, and the rest complainted low back pain and radiating leg pain.

3) In the magnetic resonance imaging of them, epidural fibrosis were 15 cases, recurrent or remained HIVD were 9, normal postoperative findings were 6, the other level of HIVD were 5, and the rest were lumbar instability and spinal stenosis.

4) The 2nd operation were performed to 8 patients. They were remained HIVD in 5 cases and the rest was epidural fibrosis.

5) In Patients whose pain free interval was less than 6 months, epidural fibrosis is were 16 cases, remained or the other level HIVD were 9 and normal postoperative MRI finding were 4 cases.