OBJECTIVE: To determine whether using the chronic care model (CCM) in an underserved community leads to improved clinical and behavioral outcomes for people with diabetes. RESEARCH DESIGN AND METHODS: This multilevel, cluster-design, randomized controlled trial examined the effectiveness of a CCM-based intervention in an underserved urban community. Eleven primary care practices, along with their patients, were randomized to three groups: CCM intervention (n = 30 patients), provider education only (PROV group) (n = 38), and usual care (UC group) (n = 51). RESULTS: A marked decline in HbA(1c) was observed in the CCM group (-0.6%, P = 0.008) but not in the other groups. The magnitude of the association remained strong after adjustment for clustering (P = 0.01). The same pattern was observed for a decline in non-HDL cholesterol and for the proportion of participants who self-monitor blood glucose in the CCM group (non-HDL cholesterol: -10.4 mg/dl, P = 0.24; self-monitor blood glucose: +22.2%, P < 0.0001), with statistically significant between-group differences in improvement (non-HDL cholesterol: P = 0.05; self-monitor blood glucose: P = 0.03) after adjustment. The CCM group also showed improvement in HDL cholesterol (+5.5 mg/dl, P = 0.0004), diabetes knowledge test scores (+6.7%, P = 0.07), and empowerment scores (+2, P = 0.02). CONCLUSIONS: These results suggest that implementing the CCM in the community is effective in improving clinical and behavioral outcomes in patients with diabetes.