Among blood pressure measurements obtained by ambulatory blood pressure monitoring (ABPM), nocturnal blood pressure has been reported to have greater prognostic significance than daytime blood pressure or 24-h blood pressure (1, 2). Blunted nocturnal blood pressure dipping (as seen in nondippers or risers) has also been shown to be a risk factor for hypertensive target organ damage (3), cardiovascular events (4), and stroke events (5). We reported that patients with exaggerated nocturnal blood pressure fall (extreme-dippers) (5) or with exaggerated morning blood pressure surge (6) had a higher risk for stroke events. These ABPM data revealed the benefits of measuring nocturnal blood pressure, both in patients with high and those with extremely low nocturnal blood pressure. However, Verdecchia et al. (7) reported that nocturnal blood pressure was not a good predictor of cardiovascular outcome in subjects with perceived sleep deprivation, which is quite relevant to ABPM, since the frequent blood pressure measurements required by this method often lead to sleep disturbance. In contrast, home blood pressure seems to be less likely to cause sleep deprivation, and can be repeated for days or even weeks. Therefore, nocturnal blood pressure assessed by a self-measurement device at home could be a possible alternative to that assessed by ABPM. Hosohata et al. (8) developed a self-measurement blood pressure device for use during sleep, and reported that 66.5% of subjects had sleep disturbance when using this device. In the subjects who reported sleep disturbance, the reproducibility of nocturnal blood pressure by the self-measurement device was lower than in those without sleep disturbance. Additionally, the reproducibility of nocturnal blood pressure