OBJECTIVE: Sleep-disordered breathing (SDB) in adults has been associated with elevated blood pressure (BP); however, the effects of severity of SDB on BP in children are uncertain. We addressed this issue by measuring BP noninvasively and continuously during sleep in children with a range of severities of SDB and in a group of nonsnoring control children. METHODS: A total of 105 children referred for assessment of SDB and 36 nonsnoring controls were studied. Routine polysomnography (PSG) was performed with continuous BP monitoring. Children were assigned to groups according to obstructive apnea/hypopnea index (OAHI). BP data were categorized as quiet awake (recorded before sleep onset), non-rapid eye movement sleep 1 and 2 combined, slow-wave sleep, and rapid eye movement sleep. RESULTS: BP during awake before sleep onset and during overnight sleep was elevated by 10 to 15 mm Hg in the 3 SDB groups compared with the control group; this finding was independent of SDB severity. BP during stable sleep (with respiratory events and movements excluded) was also elevated in the children with OSA compared with the control group. BP was elevated in rapid eye movement sleep compared with the non-rapid eye movement sleep, and heart rate was higher during wake state than in all sleep states. CONCLUSIONS: We recorded BP continuously overnight and found that SDB, regardless of the severity, was associated with increased BP during sleep and wake compared with nonsnoring control children. These findings highlight the importance of considering the cardiovascular effects of SDB of any severity in children, and the need to review current clinical management that focuses primarily on more severe SDB.