Orthostatic hypotension (OH) is defined by a drop in arterial blood pressure (BP) of at least 20 mmHg for systolic BP and 10 mmHg for diastolic BP after standing. Symptoms are generally quite typical, but may also be rather vague. Diagnosis may be easily made by the physician in his/ her office, and confirmed, if necessary, by more sophisticated measurements. Pathophysiology is generally rather complex, but mostly involves a defect in the autonomic nervous system, in its sympathetic component. Failure of peripheral vasoconstriction seems to play a more important role than the defect in reflex tachycardia. Causes of OH are multiples. OH may occur in healthy subjects, when exposed to exceptional circumstances, but is more generally associated with various diseases, either neurological disorders or pathologies characterized by hypovolemia. Medications can also aggravate the risk of OH, among which some antihypertensive or psychotropic agents. Elderly people, especially frailty subjects, are exposed to a high risk of OH, whose origin is often multifactorial, and this complication may have serious medical consequences.