Complications and side effects in any kind of surgery, especially in spine surgery, should be evaluated to prevent those problems in the future. Since retrospective studies are of minor value and randomized controlled studies for complications are impossible to perform because of ethical and legal reasons, so-called "expert opinion" has to take their place in evidence-based medicine. On the basis of an analysis of the results of three spine centers together with the opinions of experienced spine surgeons, the authors have drawn up a classification of complications in open lumbar disc surgery and recommendations on how to manage common complications such as excessive bleeding, dural opening, nerve root lesions and recurrent disc herniation. The management of intraoperative complications should have the same training in microdiscectomy instructional courses as the operation itself.