Sleep apnea, although frequently unrecognized or misdiagnosed, is neither uncommon nor trivial in its effects. Patients who complain of sleep difficulty may be treated initially with sedative-hypnotics, which only reduce arousal ability and prolong apneic episodes. Sleep apnea frequently presents with psychiatric symptoms. Once suspected, its provisional identification is not difficult, although definitive diagnosis is best done in a sleep laboratory. The symptoms, examinations and assessments, pathophysiology, and treatments are reviewed in this article in relation to the three types of apnea: obstructive, central, and mixed.