We asked the question of what are the patient level predictors (age, gender, body mass index, education, ethnicity, mental health, and comorbidity) for a sustained functional benefit at a minimum of 1 year follow-up after total knee arthroplasty(TKA). Five hundred fifty-one consecutive patients were reviewed from our joint registry between the years of 1998 and 2005. Baseline demographic data and the outcome scores of the Western Ontario McMaster University Osteoarthritis Index (WOMAC) and Medical Outcomes Short-Form 36 (SF36) scores were extracted from the database. Longitudinal regression modeling was performed to identify the predictive factors of interest. We had 27% of data points missing. The mean follow-up in our cohort was 3.0 years (range 1-8 years) and there were no revisions performed during this time. Clinical outcome scores were found to be relatively constant for 3-4 years after surgery and then demonstrated a gradual decline after that. Older age, year of follow-up, greater comorbidity, and a poorer mental health state at time of surgery were identified as negative prognostic factors for a sustained functional outcome following TKR (P<0.05). Knowledge of these factors that predict outcomes should be used in setting appropriate patient expectations of surgery.