In recent years, many metropolitan cities in India as well as in other parts of the world, there is a great demand to increase the size and the height of their municipal solid waste (MSW) landfills. The vertical capacity expansion of existing landfills by constructing a reinforced soil berm (RSB) is the most economical alternative to construct new landfills. Using limit equilibrium method and assuming three part wedge failure mechanism, analysis is conducted to evaluate the external stability of RSB. The geotechnical properties of MSW such as unit weight and shear strength characteristics vary with time as well as degree of decomposition, which is of vital concern for the slope stability. Therefore, target reliability based approach is used to estimate the probability of failure in three modes of failure viz. sliding, bearing capacity, and eccentricity of the resultant force striking the middle third of base of RSB. The properties of RSB, MSW, and foundation soil are treated as random variables. The optimum dimensions of RSB needed to maintain the stability against three modes of failure by targeting various component reliability indices are obtained. Studies have also been made to analyze the influence of various parameters on the stability of RSB for the vertical expansion in three failure modes. © ASCE 2015.