Objective: In this study, we aimed to determine the frequency of hypertension by performing 24 hours ambulatory blood pressure monitoring in children with unilateral multi-cystic disease of kidney without ipsilateral and/or contralateral kidney and/or urinary system anomalies. Methods: This study enrolled 24 patients with unilateral multi-cystic disease of kidney and age- and height-matched 20 healthy children. Blood pressure was measured by 2 approaches as follows: manual blood pressure and ambulatory blood pressure monitoring. Day-time, night-time, and 24 hours heart rate, pulse pressure, systolic and diastolic blood pressure, median arterial pressure, and systolic and diastolic blood pressure loads (%) were compared. Results: Ambulatory blood pressure monitoring measurements showed the presence of masked hypertension in 12 patients (45.8%), although 2 (8.3%) unilateral multi-cystic disease of kidney patients were hypertensive with manual blood pressure measurements. We detected that systolic blood pressure loads (%) (day-time, night-time, and 24 hours) and disatolic blood pressure loads (%) (night-time and 24 hours) were considerably higher than those of healthy children (P = .030, P = .012, P = .005, P = .012 and P = .005, respectively). Conclusion: Children with unilateral multi-cystic disease of kidney are more likely to have masked hypertension. Manual blood pressure measurements are not accurate in ruling out hypertension in children with unilateral multi-cystic disease of kidney. Ambulatory blood pressure monitoring contributes to more susceptible outcomes in proportion to manual blood pressure measurement in these patients, and it should be considered in clinical practice instead of manual blood pressure measurements.