Outcome scores are very useful tools in the field of spinal surgery as they allow us to assess a patient's progress and the effect of various treatments. The clinical importance of a score change is not so clear. Although previous studies have looked at the minimum clinically important score change, the degree of score change varies considerably. Our study is a prospective cohort study of 193 patients undergoing discectomy, decompression and fusion procedures with minimum 2-year follow-up. We have used three standard outcome measures in common usage, the oswestry disability index (ODI), the low back outcome score (LBOS) and the visual analogue score (VAS). We have defined each of these scores according to a global measure of outcome graded by the patient as excellent, good, fair or poor. We have also graded patient perception and classified excellent and good as success and fair and poor as failure. Our results suggest that a median 24-point change in the ODI equates with a good outcome or is the minimum change needed for success. We have also found that different surgical disorders have very different minimal clinically important differences as perceived by patient perception. We found that for a discectomy a minimum 27-point change in the ODI would be classed as a success, for a decompression the change in ODI needed to class it as a success would be 16 points, whereas for a fusion the change in the ODI would be only 13 points. We believe that patient-rated global measures of outcome are of value and we have quantified them in terms of the standard outcome measures used in spinal surgery.