We present here a comprehensive definition of therapeutic exergames from which a methodology to create safe exergames for real therapy pathways is derived. Three main steps are identified. (I) A clear identification of all the exercise requirements, not only in terms of goals of the therapy, but also in terms of additional constraints. Characteristic parameters for determining the challenge level and to assess progression are also defined in this phase. (II) The exercise is transformed into a Virtual Exercise, in which all the exercise elements are implemented inside a simple virtual environment. In this step the discussion between clinical and ICT teams allows maximizing the effectiveness of exergames implementation. (III) The final exergame is realized by introducing on top of the exercise all the game elements suggested by good game design to maximize entertainment. A clear line between exercises and games is drawn here. We illustrate the methodology with exergames designed for (1) balance and posture and (2) neglect rehabilitation, implemented and tested with post-stroke patients training autonomously at home. The methodology can have a broader impact as it can be applied also in other gaming fields in which the requirements go beyond entertainment. (C) 2015 Elsevier B.V. All rights reserved.