Keywords: Adherence, hypertension, chronic kidney disease, pediatric, ambulatory blood pressure monitoring Background and Objectives Children with chronic kidney disease (CKD) are susceptible to medication nonadherence, which may contribute to inadequate blood pressure control and adverse outcomes. This study aimed to determine if nonadherence is associated with longitudinal 24-hour ambulatory blood pressure monitoring (ABPM) profiles, kidney function or cardiac structure among children with CKD. Design, settings, participants, and measurements We performed secondary analyses of data from participants of the Chronic Kidney Disease in Children study (CKiD) with treated hypertension who underwent ABPM and echocardiography. Nonadherence was obtained by self-report and defined as any missed antihypertensive medication doses in the 7 days prior to the study visit. Linear regression and mixed effects models were used to assess the association of nonadherence with baseline and longitudinal ABPM profiles, estimated glomerular filtration rate (eGFR), urine protein to creatinine ratio (UPCR), and left ventricular mass index (LVMI). Results There were 508 participants who met inclusion criteria, of whom 212 (42%) were female, with median age 13 (IQR 10-16) years, median baseline eGFR was 49 (IQR 33-64) ml/min/1.73m2 and median UPCR 0.4 (IQR 0.1-1) g/g. Nonadherence to antihypertensive medications was present in 71 (14%) participants. Median follow up was 2.9 years (IQR 1.0-3.9). At baseline and in longitudinal analyses there were no significant associations between nonadherence and 24-hour ABPM profiles (baseline mean 24-hour SBP [? -0.1, 95% CI -2.7, 2.5], longitudinal [? 0.9, 95% CI -1.0, 2.8]), eGFR ( baseline [? 1.2, 95% CI -0.9, 3.4], longitudinal [? 1.2, 95% CI -0.9, 3.4]) UCPR (baseline [? 0.2, 95% CI -0.3, 0.6], longitudinal [? 0.2, 95% CI -0.3, 0.6 ]), or LVMI (baseline[? -0.3, 95% CI -2.0, 1.5], longitudinal [? -0.3, 95% CI -2.0, 1.5 ]). Conclusions In this study, antihypertensive medication nonadherence was uncommon among children with CKD, which likely represents the underperformance of self-report as an adherence measure. No significant associations were found between nonadherence and worse kidney function over time, as determined by both eGFR and UPCR or changes in cardiac structure by left ventricular mass index. Further studies of the relationship of adherence to long-term outcomes using objective measures of adherence are needed to inform targeted interventions.