BACKGROUND: Medication adherence and treatment intensification have been advocated as performance measures to assess the quality of care provided. Whereas previous studies have shown that adherence and treatment intensification (TI) of antihypertensive medications is associated with blood pressure (BP) control at the patient level, less is known about whether adherence and TI is associated with BP control at the clinic level. METHODS AND RESULTS: We included 162 879 patients among 89 clinics in the Cardiovascular Research Network Hypertension Registry with incident hypertension who were started on antihypertensive medications. Adherence was measured by the proportion of days covered (PDC). TI was defined by the standard based method with scores ranging between -1 to 1 and categorized as: -1 indicated no TI occurred when BP was elevated; 0 indicated TI occurred when BP was elevated; and 1 indicated that TI was made at all visits, even when BP was not elevated. Logistic regression models assessed the association between adherence and TI with blood pressure control (BP = 140/90 at the clinic visit closest to 12 months after study entry) at the patient and clinic levels. Mean adherence was 0.77 +/- 0.28 (PDC +/- SD) at the patient level and 0.78 +/- 0.05 at the clinic level. Mean TI was 0.026 +/- 0.23 at the patient level and 0.01 +/- 0.04 at the clinic level. At the patient level, for each 0.25 increase in adherence and TI, the odds (OR) of achieving blood pressure control increased by 28% and 55%, respectively [OR for adherence, 1.28 (1.26-1.29), and for TI, 1.55 (1.53-1.57)]. At the clinic level, each 0.04 increment increase in treatment intensification was associated with a 25% increased odds of achieving blood pressure control (OR, 1.24; 95% CI, 1.21-1.27). In contrast, there was an inverse association between increasing adherence and BP control (OR, 0.93; 95% confidence interval, 0.90-0.95). CONCLUSIONS: Patient adherence to antihypertensive medications is not associated with BP control at the clinic level and may not be suitable as a performance measure. TI is associated with BP control, but its use as a performance measure may be constrained by challenges in measuring it and by concerns about unintended consequences of aggressive hypertension treatment in some subgroups of patients.