BACKGROUND Inappropriate daily profile of blood pressure deteriorates the clinical outcome of hypertension and increases distant cardiovascular risk. The problem is important, especially in children and adolescents in whom early intervention helps to prevent complications of hypertension such as left ventricular hypertrophy and hypertensive retinopathy. OBJECTIVE To assess circadian blood pressure profile and basic determinants of inappropriate daily blood pressure variability in hypertensive children. METHODS The project was conducted retrospectively in 106 children six to 18 years of age (mean [+/- SD] 14.9+/-2.5 years) with essential hypertension and no use of antihypertensive drugs. The study group included 43 children with inappropriate daily blood pressure variability ('nondippers') and 63 controls with appropriate daily blood pressure variability ('dippers'). RESULTS Nondippers, compared with dippers, had higher systolic and diastolic blood pressure at night (systolic, 123.9+/-10.3 mmHg versus 113.9+/-8.2 mmHg; diastolic, 65.1+/-7.6 mmHg versus 59.5+/-6.5 mmHg; P<0.0001), and higher blood pressure load at night (systolic, 61.9% versus 27.6%; diastolic, 20.0% versus 9.6%; P<0.0001). Male sex increased the risk for nondipping by 2.5 times (logistic OR=2.45; 95% CI 0.87 to 6.87). However, the increase was statistically nonsignificant (P=0.08). No differences were observed between dippers and nondippers in terms of anthropometric profile, family history of hypertension, morphological and biochemical blood parameters, and birth weight. CONCLUSIONS Among hypertensive children, nondippers have a more severe degree of hypertension. Male sex increases the risk of nondipping. To assess determinants of nondipping more precisely, further clinical investigations are needed.