We investigated the working status during 2 years before and 2 years after primary knee prosthetic operation for arthrosis in order to identify preoperative factors predicting patient satisfaction, function and working capacity. 162 patients (86 women) younger than 60 years of age when operated on with a knee prosthesis during 1993 were studied. 91% of the patients returned a Nottingham Health Profile (NHP) questionnaire, and the Social Insurance Office could supply data on all patients. There was a positive association between the duration of pre- and postoperative sick-leave in the patients who returned to work. Preoperative sick-leave longer than 180 days increased the risk of postoperative disability pension, which was not found to be influenced by the grade of the work. Among the 52 patients who returned to work postoperatively, all 6 NHP functional categories were better in the patients with less than 180 days of preoperative sick-leave than in the patients with more than 180 days of preoperative sick-leave. The overall patient satisfaction was greater among patients who went back to work postoperatively. We conclude that long sick-leave before a knee prosthetic operation increases the risk of long postoperative sick-leave and disability pension and impairs the quality of life.