The clinical significance of isolated systolic hypertension in young adults (ISHY) remains a topic of debate due to evidence ISHY could be a spurious condition resulting from exageratted pulse pressure amplification in "young tall men with elastic arteries". Hence, we aimed to investigate whether ISHY is associated with an increased risk of cardivascular (CVD) mortality in a sample of 5597 young adults (49.8% men, 50.2% women) between 25 and 45 years old from the prospective population-based MONICA/KORA cohort. ISHY was prevalent in 5.2% of the population, affecting mostly men (73.1%), and associated with increased smoking, obesity, and hypercholesterolemia in comparison to participants with normal blood pressure (BP). Within a follow-up period of 25.3 years (SD ± 5.2; 141,768 person-years), 133(2.4%) CVD mortality cases were observed. Participants with ISHY had a hazard ratio (HR) of 1.89(1.01-3.53, p < 0.05) times higher risk of CVD mortality than participants with normal BP, even following adjustment for CVD risk factors. However, adjustment for antihypertensive medication (HR 0.46; 0.26-0.81, p < 0.001) and increasing height (HR 0.96; 0.93-0.99, p < 0.05) revealed independently protective effects against CVD mortality, suggesting that although ISHY is associated with an increased risk of CVD mortality, the protective effects of increasing height or antihypertensive medication should be considered in treatment rationale.