We examined the rates of postoperative complications and mortality, as recorded in a hospital discharge registry for the State of Washington for the years 1986 through 1988, for patients who had had an operation on the lumbar spine. When patients who had had a malignant lesion, infection, or fracture are excluded, there were 18,122 hospitalizations for procedures on the lumbar spine, 84 per cent of which involved a herniated disc or spinal stenosis. The rates of morbidity and mortality during hospitalization, as well as the hospital charges, increased with the ages of the patients. The rate of complications was 18 per cent for patients who were seventy-five years or older. Nearly 7 per cent of patients who were seventy-five years old or more were discharged to nursing homes. Complications were most frequent among patients who had spinal stenosis, but multivariate analysis suggested that the complications associated with procedures for this condition were primarily related to the patient's age and the type of procedure. Complications, length of hospitalization, and charges were higher for patients who had had a spinal arthrodesis than for those who had not. Over-all, operations for conditions other than a herniated disc were associated with more complications and greater use of resources, particularly when arthrodesis was performed, than were operations for removal of a herniated disc. No data on symptoms or functional results were available.