Few data are available regarding the prevalence and prognostic significance of the triple coexistence of undiagnosed systemic hypertension, diabetes mellitus, and coronary heart disease. This study aimed to evaluate the prevalence and prognostic significance of unrecognized hypertension in cardiac diabetic patients previously defined as "normotensives" over a 5-year follow-up period. The study sample comprised 11,515 patients aged 45 to 74 years with a previous myocardial infarction and/or anginal syndrome who were screened but not included in the Bezafibrate Infarction Prevention study. Among them, 9,033 were nondiabetics and 2,482, diabetics. The diabetics were divided into 3 groups: (1) 1,272 normotensives, (2) 152 patients without history of hypertension but with elevated blood pressure ("unrecognized hypertensives"), and (3) 1,058 hypertensives with established diagnosis. The prevalence of both diagnosed and unrecognized hypertension in diabetics pooled together increased from 49% to 69% when World Health Organization and new Joint National Committee-VI criteria were compared. Crude all-cause mortality was lower in nondiabetics than in diabetics (11.2% vs 22.0%; p <0.001). Among diabetics the lowest all-cause mortality was documented for normotensives (19.3%), whereas the highest mortality was observed in unrecognized hypertensives (26.3%, p = 0.003). Both unrecognized and established hypertensives demonstrated a significant stroke-related mortality excess: about four- and threefold increases in cerebrovascular accident-related death, respectively, were observed (p = 0.002). On multivariate analysis, both unrecognized and diagnosed hypertension were consistent predictors of increased all-cause mortality, with a hazard ratio of 1.28 (95% confidence interval 0.90 to 1.82) and 1.24 (95% confidence interval 1.03 to 1.49), respectively. Our findings demonstrate widespread undiagnosed hypertension in diabetic coronary patients; their 5-year mortality was significantly increased compared with normotensives, and tended to be even higher than in diabetics previously identified as hypertensives.