A total of 39 patients who had undergone microdiscectomy or percutaneous nucleotomy for lumbar disc herniation were examined after a follow-up of 5 years. The overall outcome was satisfactory in 80% of the patients treated, and only 1 (3%) patient had been reoperated during the follow-up. Clinical signs and symptoms of lumbar instability were detected in 10 (26%) patients. All these 39 patients had been examined with lumbar magnetic resonance imaging (MRI) on the day preceding the operation; the presence of disc degeneration was graded as severe, mild or non-existent depending on the visual brightness of the discs on T2-weighted images, as compared to the signal intensity of the lumbar vertebrae. None of the 12 patients with no preoperative disc degeneration in MRI suffered from postoperative clinical signs and symptoms of instability as compared to 10 (37%) of the 27 patients with mild or severe disc degeneration suffering from instability (p = 0.04). Thus, the results of the present study imply that the grade of the disc degeneration in preoperative T2-weighted MR images significantly predicted the occurrence of postoperative clinical instability.