The poor outcomes in patients who have a low-back injury that was sustained while they were on the job have been well described in many studies. The purpose of the current study was to determine the influence of Workers' Compensation on the outcome of total knee arthroplasty in forty-two patients who had been managed between January 1980 and December 1993. There were thirty-two men and ten women, and the mean age at the time of the operation was forty-eight years (range, twenty-nine to sixty-eight years). These patients were directly matched with a group of forty-two patients who were not receiving compensation. The two groups were matched with regard to nine parameters: age, gender, obesity index, preoperative deformity in the coronal plane, preoperative level of symptoms, preoperative radiographic severity according to the criteria of Ahlbäck, method of fixation, number of previous procedures, and duration of follow-up. After a mean duration of follow-up of eighty months (range, forty-eight to 178 months), the patients who were receiving compensation had a mean Knee Society score of 64 points (range, 25 to 100 points). Twelve (29 per cent) of the patients in this group had an excellent or good clinical result, and thirty (71 per cent) had a fair or poor result or had had a revision. The patients who were not receiving compensation had a mean Knee Society score of 93 points (range, 57 to 100 points) after a similar duration of follow-up. Thirty-seven patients (88 per cent) in this group had an excellent or good clinical result, and five (12 per cent) had a fair or poor result or had had a revision; the difference between the two groups with regard to fair or poor results and revisions was significant (p < 0.01). With the numbers available, no significant differences could be detected between the two groups with regard to objective measurements of range of motion and stability or with regard to radiographic alignment, the presence of radiolucent lines, or the shedding of beads. On the basis of our findings, we believe that surgeons should be aware that Workers' Compensation is one of several variables that may have an untoward influence on the perceived outcome of total knee arthroplasty.