Abnormalities in neural circulatory control may contribute importantly to the hypertensive state. The sympathetic nervous system in particular is a key mechanism for increasing blood pressure. Patients with obstructive sleep apnea have increased sympathetic activity. Obesity or other coexisting disease states do not explain the heightened sympathetic drive. This review examines the evidence linking sleep apnea with hypertension and the possible role of excessive sympathetic drive as a mediator of higher blood pressure in sleep apnea. Abnormalities in reflex circulatory control that could act to increase sympathetic activity in sleep apnea are also discussed.