Background/Aims: This study examined the association of body mass index (BMI) percentile and change in BMI percentile to change in blood pressure (BP) percentile and development of hypertension in children and adolescents. Methods: This retrospective cohort included 101,725 subjects aged 3.17 years from three health systems across the United States. Height, weight, age, sex and BP measures were extracted from electronic health records, and then age/ sex/height-adjusted BP percentiles and BMI percentiles were computed. Mixed linear regression estimated change in systolic BP percentile, and proportional hazards regression was used to estimate risk of incident hypertension associated with BMI percentile and change in BMI percentile. Results: The largest increases in BP percentile were observed among children and adolescents who became obese or maintained obesity. Over a median 3.1-year follow-up, 0.4% of subjects developed hypertension. Obese children aged 3.11 had 3.5-fold increased risk of developing hypertension compared with normal weight. Obese adolescents aged 12.17 had 3.2-fold increased risk of developing hypertension compared with normal weight. Children and adolescents who stayed obese had 5.4- and 4.8-fold increased risk of developing hypertension, respectively, compared with those who maintained a normal weight. Children who became obese and adolescents who became overweight had 2.6- and 2.3-fold increased risk of developing hypertension, respectively. Conclusion: We observed a strong, statistically significant association between increasing BMI percentile and increases in BP percentile, with risk of incident hypertension primarily associated with obesity. The adverse impact of weight gain and obesity in this young cohort over a short period of time underscores the need for effective strategies for prevention of overweight and obesity in youth to slow progression toward diabetes and cardiovascular disease later in life.