BACKGROUND: "Clinical inertia" has been defined as inaction by physicians caring for patients with uncontrolled risk factors such as blood pressure. Some have proposed that it accounts for up to 80% of cardiovascular events, potentially an important quality problem. However, reasons for so-called clinical inertia are poorly understood. OBJECTIVE: To derive an empiric conceptual model of clinical inertia as a subset of all clinical inactions from the physician perspective. METHODS: We used Nominal Group panels of practicing physicians to identify reasons why they do not intensify medications when seeing an established patient with uncontrolled blood pressure. MEASUREMENTS AND MAIN RESULTS: We stopped at 2 groups (N=6 and 7, respectively) because of the high degree of agreement on reasons for not intensifying, indicating saturation. A third group of clinicians (N=9) independently sorted the reasons generated by the Nominal Groups. Using multidimensional scaling and hierarchical cluster analysis, we translated the sorting results into a cognitive map that represents an empirically derived model of clinical inaction from the physician's perspective. The model shows that much inaction may in fact be clinically appropriate care. CONCLUSIONS/RECOMMENDATIONS: Many reasons offered by physicians for not intensifying medications suggest that low rates of intensification do not necessarily reflect poor quality of care. The empirically derived model of clinical inaction can be used as a guide to construct performance measures for monitoring clinical inertia that better focus on true quality problems. © 2007 Society of General Internal Medicine.