A prospective study of nearly 49,000 U.S. adults from NHANES 1999–2018 found that having both hypertension and type 2 diabetes simultaneously was associated with 2.46 times higher all-cause mortality and 2.97 times higher cardiovascular mortality compared to having neither condition. The burden of concurrent disease doubled from 6% to 12% over the study period. Associations were stronger in females than males, and varied by race and ethnicity. Even concurrent prediabetes and elevated blood pressure predicted up to 19% higher mortality risk. These findings highlight a critical and growing public health burden demanding targeted, context-sensitive interventions.