Effective self-management of diabetes requires considerable behavioural change and continuous support from health professionals, which can be expensive. Information technology has the potential to offer cost-effective patient support, but internet use mostly relies on the active seeking of information. Text messaging offers an ideal channel for delivering 'push' support and facilitating reciprocal communication between patient and health professional. This paper describes a participatory design methodology to develop a text message scheduling system for supporting young people with diabetes. The project illustrates how this familiar design approach can be used in a short-term project to deliver a successful medical application. Close working between clinician and software developer led to successive user-informed iterations as the clinician became more aware of the system's potential and identified barriers. The result was a reliable, functional, acceptable and usable system that was effectively implemented in its intended setting.