The impact of different levels of uncertainty associated with mechanical properties of Municipal Solid Waste (MSW) on landfill stability is evaluated in this study. Because of heterogeneous nature, different fill ages and varying degree of decomposition in MSW, it is very difficult to obtain the reliable strength parameters through experiments and above all by the great deformations that the material undergoes when stressed. Therefore, the practice of using a factor of safety to ensure adequate design has major limitations. The paper presents a framework for calculating the reliability index for the design of MSW landfills by considering the translational failure mechanism. Target reliability based approach (TRA) is used to determine the reliability index against sliding failure. Based on the reliability analysis, significant parameters that affect the design stability of landfills are discussed. The influence of coefficients of variation (COV) of unit weight and friction angle of the waste, apparent cohesion and interface shear strength between the MSW and liner material is presented. © 2013 American Society of Civil Engineers.