Background: Cardiovascular prognostic significance of relative wall thickness (RWT) in patients with diabetes has not been reported although concentric hypertrophy is common in diabetic patients. Purpose: This study was conducted to test the hypothesis that the prognostic significance of different measures of left ventricular (LV) geometric change, principally LV mass index (LVMI) and RWT, would be different in diabetic patients compared with nondiabetic individuals among Japanese hypertensive subjects. Methods: Ambulatory blood pressure monitoring and echocardiography were performed in 400 uncomplicated hypertensive individuals at baseline, of whom 379 (157 with diabetes and 222 without diabetes; mean age 67.8 ± 8.8 years) were successfully followed up for 63 ± 26 months to document cardiovascular events. We dichotomized LVMI and RWT to the highest quartile vs other 3 quartiles for further categoric analyses in diabetic and nondiabetic patients. Results: Fifty-three cardiovascular events occurred during the follow-up period. With Kaplan-Meier analysis, both diabetic and nondiabetic patients with the highest quartile of LVMI showed a significantly higher incidence of cardiovascular vents. However, the highest quartile of RWT was associated with cardiovascular events only in diabetic subjects. With Cox regression analyses controlling for age, sex, body mass index, serum creatinine, triglycerides, and clinic systolic blood pressure, RWT (per 0.01 change), but not LVMI, was associated with cardiovascular events in diabetic patients (relative risk: 1.06, 95% confidence interval 1.02-1.11; P = .008), whereas LVMI (g/m2), but not RWT, was associated with cardiovascular events in nondiabetic patients (relative risk: 1.02, 95% confidence interval 1.01-1.03; P = .005). Conclusion: In hypertensive subjects with type 2 diabetes mellitus, echocardiographic LV RWT is a predictor of cardiovascular events independent of LV mass and other confounders.