MINWii, a new serious video game targeting Alzheimer and demented patients, is a simple Music Therapy tool usable by untrained care givers. Its objective is to improve patients' self-image (renarcissization) to reduce behavioral symptoms, which are an important cause of institutionalization. With MINWii, elderly gamers use Wiimotes to improvise or play prede ned songs on a virtual keyboard. We detail our design process, which addresses the speci c features of dementia: this iterative re nement scheme, built upon qualitative, small scale experiments in a therapeutic environment, led to a shift of MINWii's original focus from creativity to reminiscence. A large majority of our patients, with mild to moderate dementia, expressed a strong interest in our system, which was con rmed by feedback from the care givers. A fully controlled usability study of MINWii is currently under way, which should lead to future research assessing its actual therapeutic impact.