Study of several field case histories showed that the difference between two and three dimensional factors of safety against slope failure is most pronounced in cases that involve a translational failure mode through low shear strength materials. Two and three-dimensional slope stability analyses of field case histories and a parametric study of a typical slope geometry revealed that commercially available threedimensional slope stability programs have some limitations including: (1) accounting for the shearing resistance along the sides of a sliding mass, (2) modeling the failure envelopes of the materials involved, and (3) considering the internal forces in the slide mass. These limitations can affect the calculated factor of safety for a translational failure mode. A new technique is presented to overcome some of these limitations and provide a better estimation of the three-dimensional factor of safety. Field case histories are presented to illustrate the use of a three-dimensional analysis in backcalculating the mobilized shear strength of the materials involved in a slope failure for use in remedial measures and design of slopes with complicated topography, shear strength, and pore-water pressures.