Obstructive sleep apnea (OSA)—also referred to as obstructive sleep apnea-hypopnea (OSAH)—is a sleep disorder that involves cessation or significant decrease in airflow in the presence of breathing effort. It is the most common type of sleep-disordered breathing (SDB) and is characterized by recurrent episodes of upper airway (UA) collapse during sleep. These episodes are associated with recurrent oxyhemoglobin desaturations and arousals from sleep. OSA associated with excessive daytime sleepiness (EDS) is commonly called obstructive sleep apnea syndrome (OSAS)—also referred to as obstructive sleep apnea-hypopnea syndrome (OSAHS). Despite being a common disease, OSAS is underrecognized by most primary care physicians in the United States; an estimated 80% of Americans with OSAS are not diagnosed. Apnea may occur hundreds of times nightly, 1-2 times per minute, in patients with severe obstructive sleep apnea, and it is often accompanied by wide swings in heart rate, a precipitous decrease in oxygen saturation, and brief electroencephalographic (EEG) arousals concomitant with stertorous breathing sounds as a bolus of air is exhaled when the airway reopens. The cardinal symptoms of sleep apnea include the "3 S ’s": S noring, S leepiness, and S ignificant-other report of sleep apnea episodes. This helpful mnemonic has proven to be valuable in teaching residents to be sensitive in the identification and appropriate referral of these patients for further study. Also helpful is if patients’ spouses or others who are close to them can attend visits. Often, sleepers are unaware that they have OSA and may in fact regard themselves as "good sleepers" because they "can sleep anytime, anywhere" (eg, in the physician’s waiting room, in traffic, in class, at his or her office). Sleepiness is one of the potentially most morbid symptoms of sleep apnea, owing to the accidents that can occur as a result of it. OSA is a very important diagnosis for physicians to consider because of its strong association with and potential cause of the most debilitating medical conditions, including hypertension, cardiovascular disease, coronary artery disease, insulin-resistance diabetes, depression, and, as mentioned, sleepiness-related accidents.