Current methods of assessing the functionality of prosthesis systems are often qualitative in nature. As such, there are issues with evaluation consistency and difficulty scaling these assessments across patient populations. Here, we describe an alternative outcome measure, the Prosthetic Hand Assessment Measure (PHAM) which quantifies the performance of manipulation tasks using body kinematics. Task performance scores are composites of individual deviation metrics and allow for standardized comparison across patient populations. It is our hope that the PHAM may aid both engineers in prosthetic systems development and clinicians in patient functionality assessment.