Many studies suggest patient factors influence TKA outcomes, but the reported data are controversial, due perhaps in part to using only postoperative scores rather than change in scores from pre- to postoperatively. We examined the effect of gender, age, diagnosis, and obesity on changes in pre- to postoperative outcome measures (Knee Society clinical rating, WOMAC, and SF-12) in a cohort of 843 consecutive knee arthroplasties in 728 patients who received the same implant (Genesis II, Smith & Nephew, Memphis, TN). Minimum followup was 5 years (mean, 9.5 years; range, 5-11 years). Kaplan Meier survivorship was 98% +/- 0.007 with any reoperation as an end point. Male and female patients had similar increases in postoperative scores. Diagnosis and obesity made no difference in postoperative increases. However, less improvement occurred in health-related quality-of-life outcomes scores with advancing age.