Masked hypertension (MH) occurs when office blood pressure is normal, but hypertension is confirmed using out-of-office blood pressure measures. Hypertension is a risk factor for subclinical cardiovascular outcomes, including left ventricular hypertrophy, increased left ventricular mass index, carotid intima media thickness, and pulse wave velocity. However, the risk factors for ambulatory blood pressure monitoring defined MH and its association with subclinical cardiovascular outcomes are unclear. A systematic literature search on 9 databases included English publications from 1974 to 2023. Pediatric MH prevalence was stratified by disease comorbidities and compared with the general pediatric population. We also compared the prevalence of left ventricular hypertrophy, and mean differences in left ventricular mass index, carotid intima media thickness, and pulse wave velocity between MH versus normotensive pediatric patients. Of 2199 screened studies, 136 studies (n=28 612; ages 4–25 years) were included. The prevalence of MH in the general pediatric population was 10.4% (95% CI, 8.00–12.80). Compared with the general pediatric population, the risk ratio (RR) of MH was significantly greater in children with coarctation of the aorta (RR, 1.91), solid-organ or stem-cell transplant (RR, 2.34), chronic kidney disease (RR, 2.44), and sickle cell disease (RR, 1.33). MH patients had increased risk of subclinical cardiovascular outcomes compared with normotensive patients, including higher left ventricular mass index (mean difference, 3.86 g/m ^2.7 [95% CI, 2.51–5.22]), left ventricular hypertrophy (odds ratio, 2.44 [95% CI, 1.50–3.96]), and higher pulse wave velocity (mean difference, 0.30 m/s [95% CI, 0.14–0.45]). The prevalence of MH is significantly elevated among children with various comorbidities. Children with MH have evidence of subclinical cardiovascular outcomes, which increases their risk of long-term cardiovascular disease.