Mobile health systems extend the Enterprise Computing System (ECS) of the healthcare provider by bringing services to the patient anytime and anywhere. We propose a methodology for the development of such extended ECSs which applies a model-driven design and development approach augmented with formal Validation and Verification (V&V) to address quality and correctness and to support model transformation. At the University of Twente we develop context aware m-health systems based on Body Area Networks (BANs). A set of deployed BANs are supported by a server. We refer to this distributed system as a BAN System. Development of such distributed m-health systems requires a sound software engineering approach and this is what we target with the proposed methodology. The methodology is illustrated with reference to modelling activities targeted at real implementations. BAN implementations are being trialled in a number of clinical settings including epilepsy management and management of chronic pain.