Trunk control is a key factor for a successful rehabilitation outcome early after stroke. Training must start early after stroke in sitting as trunk control is essential for standing and walking. A robot assisted medical chair enables therapies at various levels of trunk-control impairment. The need for such a robot assisted therapeutic chair (T-CHAIR) was identified in focus groups with various experts in stroke rehabilitation across Europe. A first prototype was developed during a project funded by the Swiss Innosuisse Agency and tested, following a user centred design approach, for its usability in a Swiss Rehabilitation clinic with physiotherapists and patients early after stroke. This project resulted in a list of requirements for a future prototype. These requirements are addressed in a follow up project with partners from Switzerland and Belgium, which receives funding from the EUs Eurostars agency. During this project, a next prototype generation has been developed and tested for its usability and effect on trunk control in patients after stroke. A significant effect has been shown with regard to clinical outcome measures by performing trunk training on the T-CHAIR.