Background: The African American Study of Kidney Disease and Hypertension was a multicenter trial of African Americans with hypertensive kidney disease randomized to an angiotensin-converting enzyme inhibitor (ramipril), a β-blocker (metoprolol succinate), or a calcium channel blocker (amlodipine besylate). We compared the incidence of type 2 diabetes mellitus (DM) and the composite outcome of impaired fasting glucose orDM (IFG/DM) for the African American Study of Kidney Disease and Hypertension interventions. Methods: Cox regression models were used to evaluate (post hoc) the association of the randomized interventions and the relative risk (RR) of DM and IFG/DM and to assess the RR of DM and IFG/DM by several pre-randomization characteristics. Results: Among 1017 participants, 147 (14.5%) developed DM; 333 (42.9%) of 776 participants developed IFG/ DM. Respective DM event rates were 2.8%, 4.4%, and 4.5% per patient-year in the ramipril-, amlodipine-, and metoprolol-treated groups. The RRs of DM with ramipril treatment were 0.53 (P=.001) compared with metoprolol treatment and 0.49 (P=.003) compared with amlodipine treatment. Respective IFG/DM event rates were 11.3%, 13.3%, and 15.8% per patient-year in the ramipril-, amlodipine-, and metoprolol-treated groups. The RRs of IFG/DM with ramipril treatment were 0.64 (P<.001) compared with metoprolol treatment and 0.76 (P=.09) compared with amlodipine treatment. The RRs of DM and IFG/DM with amlodipine treatment compared with metoprolol treatment were 1.07 (P=.76) and 0.84 (P=.26), respectively. Conclusion: Ramipril treatment was associated with a significantly lower risk of DM in African Americans with hypertensive kidney disease than amlodipine or metoprolol treatment. ©2006 American Medical Association. All rights reserved.