This study was performed to test the hypothesis that urinary levels of L-carnitine and its derivatives are enhanced in children and adolescents with hypertension and also check if analyzed parameters may serve as early markers of subclinical renal damage. The study included 112 children and adolescents (67 males and 45 females) aged median 10-18 years. Participants were divided into two groups: HT-64 subjects with confirmed primary hypertension and R-reference group-48 subjects with white-coat hypertension. Urinary Free and Total L-carnitine were determined by the enzymatic method of Cederblad. The L-carnitine levels were expressed as urinary ratio in micromole per gram creatinine (μmol/g). The urinary excretion of Total and Free L-carnitine was significantly higher in hypertensive adolescents in comparison to reference group-white coat hypertension. Other important findings were positive correlations between Free L-carnitine/cr., Total L-carnitine/cr. ratio and serum uric acid level, serum cholesterol level and systolic blood pressure. The results of this study do not explain the increased urine levels of L-carnitine. The most likely reason for excessive urinary loss was disturbed renal tubular reabsorption. It is possible to hypothesize that in hypertensive adolescents subclinical kidney dysfunction occurs. It is proposed that studies examining the concurrent plasma and urine concentration of L-carnitine and correlation with acknowledged proximal tubular markers are needed.