METHODS One hundred eight patients from a consecutive series of 125 anterior lumbar interbody fusions were invited to take part in a clinical outcome assessment (including plain radiography and magnetic resonance imaging of the lumbosacral spine) more than 10 years after the original surgery. OBJECTIVE By standardizing the reporting of outcome, to determine whether the duration of patient follow-up influences the outcome of surgery, with particular reference to the effects of compensation and psychological status. BACKGROUND The success rates of lumbar spinal fusion surgery reported in the literature vary widely. The lack of standardization of measures of patient outcome limits the value of study comparisons. Evaluation of the efficacy of spinal fusion is further compounded by the adverse effects of both compensation and psychological disturbance on the reporting of outcome. METHODS One hundred three patients agreed to take part in a clinical outcome assessment by completing a comprehensive low-back questionnaire that included demographic, compensation, and employment details. Eighty-seven of these cases also agreed to undergo radiographic evaluation and magnetic resonance imaging of the lumbar spine. Subjective assessment of outcome was based on a 10-point analog pain scale as well as patient opinion regarding the success of surgery. A more objective assessment of outcome was made using the Low-Back Outcome Score. Psychological status was determined by combining the Modified Somatic Perception Questionnaire and the Zung Depression Scale. The effects of radiologic fusion, compensation status, psychological status, and reoperation on the various outcome measures were assessed and compared with the results reported in a separate but similar series of patients with a minimum follow-up of 2 years. RESULTS Seventy-eight percent of patients rated themselves as having "complete relief" or "a good deal of relief," but only 34% fell into the "excellent" or "good" category using the Low-Back Outcome Score. The clinical outcome was not associated with the presence of radiologic fusion and was not influenced by the compensation status. Psychological disturbance at review and reoperation, however, did influence the reporting of outcome and were significantly correlated with the Low-Back Outcome Score. With the exception of the effects of compensation, these results were remarkably similar to the findings in the 2-year study. CONCLUSIONS The findings of the study suggest that the assessment of outcome of lumbar interbody fusion is strongly compounded by the psychological make-up of the patient and that this effect is maintained in the long term. However, the negative effect of compensation observed at 2 years seems to dissipate with time and becomes insignificant at 10 years.