Spinal fusion has associated complications that are similar to those resulting from any other surgical intervention. Thus, whenever a fusion is recommended as part of the care program for a patient these factors must be included in the equation. Are the positive anticipated responses of the procedure sufficient to justify subjecting the patient to the risks? In order to answer this question, the surgeon must be familiar with the complications and have a sense of their prevalence. Much of this data is not really available today, but when possible an attempt for perspective will be offered. A text such as this prepared for orthopaedists, neurosurgeons, fellows and residents will not include complications frequently managed by alternative medical personnel. However, we would expect the reader to be aware of the following complications: hepatitis, renal failure, AIDS, antibiotic toxicity, diffuse intravascular coagulopathy, urinary tract infection, inappropriate antidiuretic hormone release, transfusion reactions, cardiac failure, malignant hyperthermia, drug dependency, atelectasis, pulmonary edema, and pulmonary embolus.