Size at birth and early postnatal growth rates appear to be important determinants of cardiovascular diseases. We examined whether intrauterine growth restriction or the subsequent catch-up postnatal weight gain leads to higher blood pressure in early life to confirm that size at birth and early postnatal growth rates appear to be important determinants of blood pressure changes in early life. Of 407 children born between December 2001 and November 2002 in hospital based-birth cohorts, 102 were followed up at 3 years of age (24.2%) at Ewha Womans University Hospital in Seoul, Korea. At 3 years of age, those who had a low birth weight still belonged in the lower-weight group than the others. The subjects' systolic blood pressure was correlated with their current weight (r = 41) and weight gain (r = 0.39), but not with their birth weight. Those with a higher current weight and higher weight gain based on birth weight (conditional weight gain) had the highest blood pressure. Systolic blood pressure increased by 0.2mm Hg for every 100-g increase in weight at 3 years and, independently, by 1.5mm Hg for every 100-unit increase in conditional weight gain. This study suggests that birth weight is not directly associated with blood pressure, but accelerated growth, which occurs mostly in those born with a low birth weight, seems to affect blood pressure in early life.