Objective: To assess the effects of two types of microprocessor-controlled prosthetic knee joints (MPKs) on perceived performance and everyday life activity level. Design: Randomized cross-over trial. Subjects: Thirty persons with a unilateral above-knee amputation or knee disarticulation classified as Medicare Functional Classification Level-2. Methods: Participants were measured in 3 conditions, i.e. using a mechanically controlled prosthesis, an MPK featuring a microprocessor-controlled stance and swing phase (MPKA), and an MPK featuring a microprocessor-controlled stance phase (MPKB). Subjects' perceived performance regarding prosthesis use was measured with the Prosthesis Evaluation Questionnaire. Subjects' activity level was quantified using accelerometry. As high within-group variability regarding subjects' functional performance was expected to impede detection of possible effects of an MPK, data were analysed for the total group and for 3 subgroups of participants. Results: Participants' perception regarding ambulation, residual limb health, utility, and satisfaction with walking were significantly higher in the MPKA condition compared with the mechanical knee joint condition. Participants' activity level was similar in all knee joint conditions. Conclusion: Although Medicare Functional Classification Level-2 amputees report benefitting in terms of their performance from using an MPK, this is not reflected in their actual daily activity level after one week of using an MPK.