BACKGROUND: Despite large numbers of studies and literature reviews about guideline implementation, it remains unclear whether and how clinical guidelines can be used to improve the quality of medical care. This study sought to learn whether these studies and reviews have recognized the importance of systems thinking and organizational change for implementation. METHODS: A literature search was conducted for systematic reviews of guideline implementation or practice improvement studies. Each review was studied for the extent to which it identified or discussed the value of systems changes, organizational support, practice environmental factors, and use of a change process. RESULTS: Forty-seven good-quality systematic reviews were found. They largely concurred that using reminders and perhaps using feedback in the course of clinical encounters were the most effective ways of implementing guidelines. However, these same reviews rarely identified these strategies as systems changes, and there was little discussion about any need for organizational support or attention to various environmental variables that might affect implementation. The change process required to introduce a new or changed practice system received even less attention. CONCLUSION: Reviews of guideline implementation trials have focused on how to change the behavior of individual clinicians. There has been little attention to the impact of practice systems or organizational support of clinician behavior, the process by which change is produced, or the role of the practice environmental context within which change is being attempted. New attention to these issues may help us to better understand and undertake the process of improving medical care delivery.