Blood pressure (BP) during sleep (i.e., nocturnal BP) is an independent risk factor for cardiovascular outcomes. Given that factors associated with nocturnal BP differ from those associated with awake BP, studies need to clarify the complete physiological background for nocturnal BP elevation to achieve 24-h BP control. Evidence suggests that obstructive sleep apnea is associated with nocturnal BP, though its effect on BP is not strong enough to increase mean levels of nocturnal BP. Nocturia, a manifestation of salt sensitivity, has been strongly associated with both sleep apnea and nocturnal BP, indicating that the association between obstructive sleep apnea and nocturnal BP may be partly mediated by nocturia. Instead, we found that sleep apnea was significantly associated with morning BP, though their relationship has received less attention. The association between sleep apnea and morning BP deserves further investigation to reduce cardiovascular disease risk.