The current sustained trend toward increased miniaturization has created a need for models that can be used to accurately predict process forces at the microscale level. These process models should adequately incorporate size effects (i.e. variations in the material and process parameters with miniaturization). There are two types of size effects, specimen size effects and grain size effects (Armstrong 1961). In this paper a new process model is developed for the prediction of the peak force for a microscale forward extrusion process. This model is based on an upper bound slab analysis model that is used at the macroscale level [Altan et al. (1983)]. This new microscale model was developed to account for increased shear deformation in the center of the pins that is observed as the grain size is increased and/or the specimen size reduced, The microscale model provided more accurate predictions of the peak extrusion force for the microscale specimens.