Introduction/Background: Outcomes assessment in orthopaedics has advanced over the last decade. There are various different methods that can be used in a clinical setting to assess function and pain. During a clinical consultation, a simple, quick and restricted history, examination and review of investigations can be undertaken. Aim: I wished to ascertain whether function improved as a result of knee or hip joint replacement, and which of the commonly used existing methods of assessing function are of most value in this context. Methods: To achieve this aim, I recruited a broad spectrum of patients about to undergo primary or revision surgery for hip (n=42) or knee (n=51) joint disease. The study design was an observational cohort study, with data collection points pre-operatively and at 3 months post-operatively. Results: Most participants had less pain and better function 3 months after surgery than pre-operatively. However, the mean scores obscured the fact that several participants showed no improvement or worsening on some of the scores. Participants with the worst functional scores at baseline were most likely to improve. Performance tests showed less overall improvement than self-assessment measures. Overall walking times correlate well with all the other scores, with the exception of the Short Form-12 mental component score and American Knee Society Knee Score. However, in hip participants those with the best Harris Hip Scores did not have the best walking times, or the best Western Ontario and McMaster Arthritis Index or best Short Form-12 scores. Flexion beyond 90 degrees did not correlate with functional scores at the hip. Both inter and intra-rater reliability findings were good for both the Harris Hip Score and American Knee society score. Conclusions: Differences are identified in the outcome between different health status instruments commonly used in assessing function by self report questionnaires, surgeon based and performance based assessments. More research is needed to identify either the best method or more likely different instruments to identify important specific domains after hip and knee joint surgery.