Background <p>Kidney scarring (KS) secondary to urinary tract infections is a common cause of secondary hypertension in children. We investigated the association between serum cystatin C and hypertension in children with KS using 24-h ABPM.</p> Methods <p>One hundred eleven children (aged 6–18 years) with DMSA-confirmed KS were included. All patients underwent 24-h ABPM, and serum cystatin C, creatinine, creatinine-based eGFR, and cystatin C-based eGFR were calculated. Hypertension was defined according to current AAP and ESH recommendations, using age and gender/height-specific threshold values in ABPM. The relationships between hypertension, biochemical parameters, and scar severity were assessed using multivariate analysis. No participant was taking antihypertensive medication at the time of ABPM.</p> Results <p>Hypertension was detected in 36.9% (<i>n</i> = 41) of patients. Serum cystatin C levels were significantly higher in the hypertensive group (1.06 mg/L vs. 0.94 mg/L, <i>p</i> = 0.004). When assessed for kidney function, both creatinine-based eGFR (<i>p</i> = 0.044) and cystatin C-based eGFR (67 [42–183] vs. 74.9 [30.9–183] mL/min/1.73 m², <i>p</i> = 0.004) were significantly lower in the hypertensive group than in the normotensive group. Mean systolic nocturnal dip was &lt; 10% (non-dipper) in both groups. In multivariate logistic regression, only high-grade scarring (Grades 3–4) remained an independent risk factor, increasing the risk of hypertension by 3.44-fold (95% CI: 1.45–8.16, <i>p</i> = 0.005).</p> Conclusions <p>High-grade scarring is a significant independent risk factor for hypertension. Although cystatin C reflects the severity of kidney damage, its association with hypertension depends on the scar burden. Since circadian rhythm disturbances (non-dipping) are common, even in children with normal office blood pressure, ABPM may be necessary for monitoring those with KS.</p> Graphical abstract <p></p>