There are no available guidelines for the diagnosis of meniscal tears in patients with osteoarthritis of the knee. The goal of the present study was to prospectively study a cohort of such patients referred for arthroscopy and develop a clinical prediction rule to select patients who would benefit from arthroscopy. Patients with osteoarthritis of the knee refractory to conservative medical treatment were selected for arthroscopic evaluation. A standardized assessment protocol was administered to each patient and repeated by a second observer when feasible to permit calculation of the kappa coefficient ($\kappa$) for interobserver agreement. Arthroscopic determination of unstable meniscal tears was recorded by one observer who reviewed a video recording and was blinded to preoperative data based on objective criteria. Those variables which had the highest interobserver agreement and the strongest association with meniscal tear by univariable methods were then entered into a logistic regression model. This study underscored the difficulty in using clinical variables to predict unstable medial meniscal tears which were addressed at arthroscopy. (Abstract shortened by UMI.