Background: The impact of diagnosing pediatric hypertension based on all three-24-hour, day and night ambulatory blood pressure (ABP) thresholds (combined ABP threshold) vs. conventionally used 24-hour ABP threshold is not known. Methods: In this cross-sectional, retrospective study from a tertiary care outpatient clinic, we evaluated the diagnosis of hypertension based on the 24-hour European Society of Hypertension (ESH) and combined ESH ABP thresholds in untreated children with essential hypertension. The American Academy of Pediatrics (AAP) and Fourth Report thresholds were used to classify office blood pressure (OBP). Results: In 159 children, aged 5-18 years, the 24-hour ESH and combined ESH thresholds classified 82% (95th confidence interval (CI) 0.68, 0.97) ABP similarly with the area under the curve (AUC) of 0.86 (95th CI 0.80, 0.91). However, the AUC of the 2 ABP thresholds was significantly higher in the participants with office hypertension than office normotension, with OBP classified by the AAP (AUC 0.93, 95th CI 0.84, 0.98 vs. 0.80, 95th CI 0.71, 0.88) or Fourth Report (AUC 0.93, 95th CI 0.83, 0.98 vs. 0.81, 95th CI 0.73, 0.88) threshold. With OBP classified by the either OBP threshold, the combined ESH threshold diagnosed significantly more masked hypertension (MH) (difference 15%, 95th CI 4.9, 24.7; P = 0.00); however, the diagnosis of white coat hypertension (WCH) by the 2 ABP thresholds did not differ significantly (difference 4%, 95th CI 1.8, 10; P = 0.16). Conclusions: In children with essential hypertension, the 24-hour and combined ESH thresholds have a stronger agreement for diagnosing WCH than MH.