Obstructive sleep apnea syndrome (OSAS) is a common but still underrecognized disorder. It affects 2% to 4% of middle-aged adults, a significant proportion of whom are female. The spectrum of clinical presentations of OSAS and their severity is variable, ranging from neurocognitive complaints to cardiorespiratory failure. OSAS has a significant impact on quality of life, cardiovascular morbidity, and mortality. Its major sequelae include daytime somnolence and its consequences (motor vehicle accidents, poor work performance, disrupted social interactions), systemic and pulmonary hypertension, and ischemic heart disease. Treatment of OSAS results in improvement in symptoms, quality of life, and blood pressure control, and may improve mortality. An expansion of our understanding of this condition has resulted in increased awareness of its consequences, but the recognition of OSAS in clinical practice is still delayed. Identification of these patients in clinical practice requires attention to risk factors (history of snoring and witnessed apneas, obesity, increased neck circumference, hypertension, family history) and careful examination of the upper airway. Clinical impression alone, however, has poor (50% to 60%) sensitivity and specificity (63% to 70%) and the diagnosis is usually obtained on polysomnography. Physicians and other health care professionals need to be aware of the progress made in this area and recognize the necessity for prompt evaluation and treatment of these patients.