The ability to objectively measure an amputee's walking activity over prolonged periods can provide clinicians with a useful means of evaluating their patients' outcomes. The present study aimed to validate the temporospatial data output from a commercially available ambulatory activity monitor (PAM, Ossur) fitted to trans-tibial and trans-femoral amputees, against data that was simultaneously captured from a three dimensional motion analysis system (Qualisys Medical AB, Gothenburg, Sweden). Results indicate that the PAM monitor provides accurate measures of temporospatial aspects of amputee gait for walking speeds above 0.75 m/s.