Among youth, hypertension is no longer a rare disease, affecting about 7 million children and adolescents. Numbers are increasing with the evolving pediatric obesity epidemic in the US. More adolescents than children have primary hypertension, which tracks into adulthood and has been linked with preclinical indicators of adverse cardiovascular events in adults. Early prevention and intervention efforts are needed to address this increasing public and individual health problem. The purpose of this project is to evaluate the immediate and sustained impact of a 3-month clinic-based behavioral nutrition intervention emphasizing a diet high in fruits, vegetables, and low fat dairy, and low in fat and sodium (the DASH intervention) versus routine nutrition care on changing dietary knowledge, self-efficacy, diet quality and blood pressure in adolescents with pre-hypertension or hypertension. The DASH intervention will include a printed participant manual, 1 individual counseling session with a dietitian, 4 mailings and 10 telephone calls on behavioral strategies to promote dietary change. Routine care will include 1 individual counseling session with a dietitian on dietary guidelines consistent with those of the National High Blood Pressure Education Program. Adolescents with prehypertension or hypertension will be randomly assigned to the DASH intervention or routine nutrition care after pre-treatment assessment. Post-treatment and at 3-month follow-up, outcome measures will be assessed including nutrition knowledge, self-efficacy, dietary intake, and blood pressure. Our expectations are that the DASH intervention will significantly improve dietary knowledge, self-efficacy, dietary quality and blood pressure in adolescents with elevated blood pressure compared to that observed as a result of routine nutrition care. The findings from this study are expected to improve the manner in which hypertension among adolescents is being treated in the clinical setting and contribute to the enhancement of the cardiovascular health of the target population.