This thesis studies the use of off-the-shelf motion sensing technology in physical therapy rehabilitation. The aim of this thesis is to evaluate how suitable existing commercially available video gaming consoles are for use in physical therapy and explore the challenges associated with creating custom therapeutic systems based on existing platforms.A set of qualitative data gathering activities were selected; observations, workshops, interviews and prototyping. Five physical therapists working at hospitals were selected as participants. Through these activities empirical data was obtained for further analysis and discussion.The participating therapists suggested that existing games were only to a small extent directly applicable as treatment methods, hence custom tailored games should be developed. Patients have very different needs, and the existing games are developed with mainly healthy people in mind, and therefore it is not obvious that they are applicable as rehabilitation treatment. To develop games for patients that need physical therapy, knowledge in this field is needed - hence the involvement of five specialists cooperating with a system developer. The findings indicate that games to be used in physical therapy ideally need to be extremely customizable by the therapists to allow adjustments to individual patient needs. This leads to a set of design guidelines for developing rehabilitation games with motion sensing input devices. The physical therapists in this thesis are positive towards introducing Nintendo Wii to their patients, and see great potential in using the Wii as a tool in their future work.