BACKGROUND: Nonadherence is common in children with chronic kidney disease (CKD). This may contribute to inadequate blood pressure control and adverse outcomes. This study examined associations between antihypertensive medication nonadherence, ambulatory blood pressure monitoring (ABPM) parameters, kidney function, and cardiac structure among children with CKD. METHODS: We performed secondary analyses of data from the CKD in Children (CKiD) study, including participants with treated hypertension who underwent ABPM, laboratory testing, and echocardiography biannually. Nonadherence was defined by self-report of any missed antihypertensive medication 7 days prior to the study visit. Linear regression and mixed-effects models were used to assess the association of nonadherence with baseline and time-updated ABPM profiles, estimated glomerular filtration rate (eGFR), urine protein to creatinine ratio (UPCR), and left ventricular mass index (LVMI). RESULTS: Five-hundred and eight participants met inclusion criteria, followed for a median of 2.9 years; 212 (42%) were female, with median age 13 years (IQR 10-16), median baseline eGFR 49 (33-64) ml/min/1.73 m and median UPCR 0.4 (0.1-1.0) g/g. Nonadherence occurred in 71 (14%) participants. Baseline nonadherence was not significantly associated with baseline 24-h ABPM parameters (for example, mean 24-h SBP [β - 0.1, 95% CI - 2.7, 2.5]), eGFR (β 1.0, 95% CI - 0.9, 1.2), UCPR (β 1.1, 95% CI - 0.8, 1.5), or LVMI (β 0.6, 95% CI - 1.6, 2.9). Similarly, there were no associations between baseline nonadherence and time-updated outcome measures. CONCLUSIONS: Self-reported antihypertensive medication nonadherence occurred in 1 in 7 children with CKD. We found no associations between nonadherence and kidney function or cardiac structure over time. A higher resolution version of the Graphical abstract is available as Supplementary information.