For several years predictivemaintenance has been gaining popularity as a method for preventing costly and time-consuming machine breakdowns. Vibration analysis is the cornerstone of predictive maintenance programs@ and the equations for calculating expected vibration frequencies for bearings and toothed gear sets are widely available. Cycloidal reducers present a special case due to the nature of their reduction mechanism. This paper will describe a method for utilizing vibration analysis in order to identify a defective cycloidal ring gear housing@ disc@ and eccentric bearing.