BACKGROUND: Studies show that it is difficult to achieve blood pressure (BP) targets among people with diabetes. Methods to improve BP control are needed. A quality improvement (QI) collaborative was established to improve systolic BP (SBP) control in persons with diabetes. METHODS: A longitudinal study with a three-phase QI collaborative as the intervention was conducted with 51 primary care practices within 12 health care organizations in the United States. Baseline, 6-, and 12-month posteducation performance data were collected. Phase 1 began in October 2006, and all sites completed all three phases by June 2008. Sites participated on four collaborative conference calls to discuss shared data and individual site activities, as well as on monthly calls with their project consultant. Some 624 staff participated in interactive education programs, and data were collected on 11,510 patients with diabetes. FINDINGS: All site champions stated that the collaborative supported process changes and engaged stakeholders and patients, focused staff on accurate BP measurement and treatment options, and served to identify and address gaps in outcomes. Mean SBP significantly improved from baseline (130.4 mmHg) to 6 months (127.4 mmHg; p < .001) and to 12 months (128.6 mmHg; p < .001). The proportion of patients with SBP < 130 mmHg increased from baseline (47.3%) to 6 months (56.4%; p < .001) and to 12 months (53.1%; p < .001). The proportion of patients with BP < 130/80 mmHg increased from baseline (36.8%) to 6 months (45.1%; p < .001) and to 12 months (42.2%; p < .001) CONCLUSIONS: A QI collaborative that provides focus, structure, and strategies to help health care organizations customize and standardize processes related to BP management can improve BP control in patients with diabetes.