Aims:We sought to develop and validate a classiþcation system for assessing PFJ status prior to revision surgery. Methods: The classiþcation system grades the condition of the PFJ by describing both the patella bone stock and the patello-femoral tracking. The system was analysed for its reliability by assessing both intra- and inter-observer variability. From our database of 110 patients who underwent revision knee arthroplasty, 66 cases were selected at random. Each patient had both pre and post-operative radiographs to classify. 145 sets of radiographs, each set consisting of an AP, lateral and skyline patella view, were studied. Three clinicians graded all radiographs according to the classiþcation system on 2 separate occasions. These assessments were performed at least 6 weeks apart. The results were analysed by an independent observer who was blinded. Both intra- and inter-observer agreement was quantiþed using kappa values. Results: Inter-observer kappa values between observers A& B, B& C and C& A were 0.89, 0.96 and 0.82 respectively. Intra-observer kappa values were 0.94, 0.87 and 0.97 for the 3 clinicians. This indicates excellent levels of agreement. Conclusions: The proposed classiþcation system provides a convenient, spe-ciþc, descriptive and reproducible method of denoting PFJ status. Our system may be used to accurately communicate and compare PFJ characteristics. This will aid planning of surgical intervention and allow comparison of results and techniques in revision knee arthroplasty.