PURPOSE: The Chronic Care Model (CCM) provides a conceptual framework for transforming health care for patients with chronic conditions; however, little is known about how to best design and implement its specifics. One large health care organization that tried to implement the CCM in primary care provided an opportunity to study these issues. METHODS: We conducted a qualitative, comparative case study of 5 of 18 group clinics 18 to 23 months after the implementation began. Built on knowledge of the clinics from a previous study of advanced access implementation, data included in-depth interviews with organizational leaders and varied clinic personnel, observation of clinic care processes, and review of written materials. RESULTS: Relatively small and highly variable care process changes were made during the study period. The change process underwent several marked shifts in strategy when initial efforts failed to achieve much and bore little resemblance to the change process used in the previously successful large-scale implementation of advanced access scheduling. Many barriers were identified, including too many competing priorities, a lack of specificity and agreement about the care process changes desired, and little engagement of physicians. CONCLUSION: These findings highlight specific organizational challenges with health care transformation in the absence of a blueprint more specific than the CCM. Effective models of organizational change and detailed examples of proven, feasible care changes still need to be demonstrated if we are to transform care as called for by the Institute of Medicine.