Objective: To study the influence of a transition from a non-microprocessor controlled to the Rheo Knee® II on quality of life, balance confidence and measures of mobility. Design: Randomised crossover trial. Setting: Research department of a rehabilitation centre. Subjects: Persons with a transfemoral amputation or knee disarticulation (n=10). Interventions: Participants were assessed with their own non-microprocessor controlled knee and with the Rheo Knee® II. The low-profile Vari-Flex with EVO foot was installed in both knee conditions, followed by eight weeks of acclimatisation. The order in which knees were tested was randomised. Main measures: Prosthesis Evaluation Questionnaire with addendum, Activities-specific Balance Confidence scale, Timed “up & go” test, Timed up and down stairs test, Hill Assessment Index, Stairs Assessment Index, Standardized Walking Obstacle Course and One Leg Balance test. Results: Significant higher scores were found for the Rheo Knee® II on the Residual Limb Health subscale of the Prosthesis Evaluation Questionnaire when compared to the non-microprocessor controlled prosthetic knee (median [interquartile range] resp. 86.67 [62.21-93.08] and 68.71 [46.15-94.83]; P=0.047) In addition, participants needed significantly more steps to complete an obstacle course when walking with the Rheo Knee® II compared to the non-microprocessor controlled prosthetic knee (median [interquartile range] resp. 23.50 [19.92-26.25] and 22.17 [19.50-25.75]; P=0.041). On other outcome measures, no significant differences were found.