We reviewed the records of 243 patients treated at 271 disc levels to determine the incidence of side effects and complications of percutaneous nucleotomy. In our early experience there were 7 technical failures (2.5% of all attempts), of which 6 were at the 5th disc level. The success rate dropped from 67% at 3 months to 60% 1 year after treatment due to recurrences in 16 patients (6.6%). Extruded or sequestered fragments were found in 6 patients (2.4%), and may have been caused by nucleotomy. However, only one was accompanied by aggravation of symptoms. Discitis was seen in 2 patients (0.8%), both treated at two separate disc levels. About half the patients experienced increased low back pain, mean duration 9 days, after treatment, and 3 (1.2%), of whom 2 also had nonorganic disorders, needed admission to hospital because of severe pain. Mild spasm and a sensation of instability were noted by 9.6% and 25% of the patients respectively. Injury to nerves, bowels, vessels or ureters or a dural leak never occurred. The study confirms earlier reports that the rate of serious complications is low.