ObjectiveA blunting of the nocturnal fall in arterial blood pressure is found in a minority of patients (nondippers) with essential hypertension. We tested whether sleep-disordered breathing (snoring and apnea or hypopnea) might explain such a finding for male patients, among whom its prevalence is much higher.Setting and patientsWe studied 100 new cases of hypertension in men, observed consecutively by a local group of general practitioners and diagnosed essential hypertensives in a referral clinic. By using 24 h ambulatory blood pressure monitoring with a SpaceLabs 90207 device, 15 patients were classified initially nondippers (daytime ambulatory blood pressure ≥ 136/87 mmHg; night-time decrease by < 10% of the daytime mean), but only 11 were confirmed to be nondippers by continuous blood pressure monitoring with a Finapres device. Ten dippers matched by age, body mass index and mean 24 h blood pressure were used as controls.Main outcomemeasures Parameters of nocturnal polysomnography.ResultsDuring polysomnography, the nondippers exhibited a blunting of the sleep-related fall in blood pressure and an increased variability in blood pressure associated with sleep-disordered breathing (heavy snoring for all, with an apnea or hypopnea index > 10 in 10 cases). Six of the control patients breathed normally and four snored nonapneically. There was a normal fall in nocturnal blood pressure in all 10 cases.ConclusionsThe nondipper condition appears to be associated with undiagnosed apneic snoring for an unselected population of previously untreated male subjects with a diagnosis of essential hypertension. Ambulatory blood pressure monitoring of such patients is of limited diagnostic value.