Despite recommendations that patients be involved in the design and testing of health technologies, few reports describe how to involve patients in systematic and meaningful ways to ensure that applications are customized to meet their needs. User-centered design is an approach that involves end users throughout the development process so that technologies support tasks, are easy to operate, and are of value to users. In this article, we provide an overview of user-centered design and use the development of Pocket Personal Assistant for Tracking Health (Pocket PATH) to illustrate how these principles and techniques were applied to involve patients in the development of this interactive health technology. Involving patient-users in the design and testing ensured functionality and usability, therefore increasing the likelihood of promoting the intended health outcomes.