ABSTRACT: Microprocessor knee (MPK) prostheses have been shown to reduce energy expenditure at different gait speeds in a number of studies. However, the few comparisons between the use of non-MPK and MPK prostheses from multiple manufacturers limits the understanding of MPK prostheses as a type of prosthesis. This systematic review examined studies comparing energy expenditure in users of non-MPK and MPK prostheses. After potential studies were identified, screened, and assessed for eligibility, seven studies involving MPK prostheses from three manufacturers were selected for quality and bias assessment. A pattern of energy reduction with the use of a microprocessor compared with non-MPK prostheses emerged from the reviewed studies, although conclusions must be made with caution because of low study quality.