A total of 190 patients treated microsurgically for a virgin single level lumbar disc herniation were examined physically after a mean follow-up period of 3 years (range 21-68 months). Included were 99 (52%) men and 91 (48%) women with a mean age of 42 years. During the observation period, sciatica had completely recovered or markedly diminished in 172 (90%) patients, and 142 (75%) patients had returned to work. However, as many as 29% of the patients occasionally suffered from low back pain. Clinical examination revealed various signs and symptoms of segmental instability of the lumbar spine in 22% of the surgical patients. There was a significant association between postoperative instability and unsatisfactory long-term outcome: of the 42 patients with instability, 62% suffered from low back pain and 45% were on sick leave or retired because of the back, while the corresponding numbers for those patients without instability were 20% and 8%, respectively (p < 0.0001). Moreover, the mean value of the Oswestry index in instability patients was as high as 34% (SD 12), indicating moderate disability, whereas a significantly (p = 0.0001) lower Oswestry Index 16% (SD 13), indicating minimal disability, was detected in patients without instability.