The aim of this study, the YOung TAiwanese Cohort (YOTA) Study, was to investigate the relationship between a childhood overweight/obese status and young adult preclinical atherosclerosis, including assessments of the carotid intima-media thickness (CIMT) and prehypertension or hypertension. From among children who participated in the 1992-2000 mass urine screening program in Taiwan, we recruited 303 subjects with an elevated blood pressure (EBP) and 486 subjects with a normal BP in childhood during the period of 2006-2008. These 789 young adults received health check-ups for cardiovascular health, including examinations of blood and urine parameters, anthropometrics, BP and the CIMT, a subclinical cardiovascular risk index. Data analyses were used to evaluate the associated risks in both childhood and young adulthood. The school students with a childhood overweight/obese status had a higher risk of prehypertension or hypertension, with a relative risk of 3.20 (1.40-7.33) for being overweight and 6.51 (3.36-12.63) for being obese in young adulthood at an average age of 21. A childhood overweight/obese status also predicted a higher risk of having a thicker CIMT, with a relative risk of 2.82 (1.26-6.28) and 4.17 (2.21-7.85) for being overweight and obese in adulthood, respectively, after a mean follow-up of 8.5 years. The body mass index exhibited a consistent trend from childhood to adulthood, with an adjusted R square of 0.551. The participants who were not overweight/obese in childhood also demonstrated a higher risk of prehypertension or hypertension if they became overweight or obese in adulthood. This study highlights the importance of preventing and treating an overweight or obese status in childhood for the primary prevention of cardiovascular disease in adulthood.