Obstructive sleep apnea (OSA) is a disorder in which there is repetitive collapse and closing of the pharynx during sleep. There is growing evidence to suggest that this disorder is a major cause of essential hypertension (EH) and that successful treatment of OSA can reduce the blood pressure (BP) significantly. In addition many other patients with EH have milder forms of sleep related breathing disorders (SRBD) like snoring, and upper airway resistance syndrome (UARS) which, while not as severe as OSA, may be severe enough to also cause systemic hypertension. We therefore propose a unifying hypothesis-that many patients with EH may have sleep related breathing disturbances (SRBD) and treatment of these disorders may improve the BP. SRBD could also explain many of the epidemiological, clinical, hereditary, biochemical, hematological and physiological characteristics seen in EH. In addition, many types of secondary hypertension (those caused by excessive alcohol intake, chronic renal failure, diabetes, hypothyroidism or acromegaly) have a higher than normal prevalence of OSA and OSA may contribute to the hypertension and organ damage found in these conditions as well. Thus SRBD may play an important role in the production of many cases of essential and secondary hypertension, and their early detection and treatment could reduce the hypertension and organ damage seen in these conditions.