We have evaluated the clinical outcome of 45 consecutive patients who underwent percutaneous nucleotomy for a single-level disc herniation. Included were 28 (62%) woman and 17 (38%) men, with a mean age of 46 years. The mean postoperative follow-up time was 2 years. Intra-operatively, disc herniation was graded as a protrusion in 23 (51%) patients and as a prolapse in 22 (49%) patients. During the follow-up, sciatic pain completely recovered or markedly diminished in 38 (84%) patients and 35 (78%) patients returned to work. The occupational outcome of the patients operated on for a protrusion was inferior to that of the patients operated on for a prolapse: only 22% of the patients who underwent surgery for a protrusion reported to manage their work well, while as many as 41% of those with a prolapse managed well (p = 0.04). Pre-operatively, clinical examination revealed segmental instability of the lumbar spine in 11 (24%) patients. There was a significant association between instability and unsatisfactory long-term outcome: of the patients with pre-operative instability, 45% were postoperatively retired or on sick leave because of the back, as compared to 15 % of the 34 patients without instability (p = 0.03). Furthermore, patients with instability suffered from sciatica and low back pain significantly (p = 0.02) more often than those without instability. Surgical complications were infrequent. There were no nerve root lesions and no vascular injuries. Postoperative discitis developed in 2 (4%) patients. Of all patients, only 1 (2%) has been re-operated on for a recurrent disc.