Despite advances in health care over the past decades, medical errors and omissions remain significant threats to patient safety and health. A large number of these mistakes are made by trainees, persons who are just beginning to build the case-based experiences that will transform them from novices to expert practitioners. Clinicians use both intuitive and deductive problem-solving skills in caring for patients and they acquire expertise in applying these skills through interaction with many and varied cases. The contemporary heath care environment, with decreased lengths of stay for patients and reduced duty hours for trainees, makes getting optimal patient exposure difficult. Virtual patients (VPs), online, interactive patient cases, may help close the case exposure gap. Evidence has shown that VPs improve clinical reasoning skills, but no formal instructional design theory of VPs has been advanced. The goal was to conduct formative research to develop an instructional design theory of VPs to help novice clinicians cultivate clinical reasoning and diagnostic skills. The instructional design theory, goal-based scenarios (GBS), grounded in the learning theory, Case-based Reasoning, provided methods that promised to be appropriate to the goal. An existing, two-module, multimedia VP, Matt Lane, A Pressure Ulcer Prevention Virtual Patient, was tested with 10 medical trainees to determine which methods of GBS it incorporated and which of its methods were not part of GBS. Leaners' experience of what worked and didn't work to promote learning in the VP was analyzed. The VP was found to incorporate all GBS methods and one significant method, the Life Model, that was not part of GBS. The Life Model Method involved replicating, with a high degree of fidelity, the experiences of a real patient in creating the VP scenario. Recommendations for customization of GBS for VPs included more explicit advertisement of learning goals and leverage of Internet search engines to provide just-in-time resources to support problem-solving. Incorporation of the Life Model was also recommended along with the Simplifying Conditions Method from Elaboration Theory to manage the complexity inherent in the Life Model. The resultant, enhanced GBS theory may be particularly relevant in teaching patient-centered care.