Syncope, the transient loss of consciousness and postural tone, is both a sign and a syndrome and may result from very diverse causes. Over the last decade, considerable attention has been focused on neurocardiogenic syncope, also known as vasovagal syncope. Research has demonstrated that the disorder is one aspect of a much broader group of disturbances of the autonomic nervous system that may lead to hypotension, orthostatic intolerance, and ultimately syncope. Recent discoveries have caused us to reevaluate our classification of autonomic disorders and to develop a new system that reflects current knowledge. A basic understanding of syncope and related disorders is essential to diagnosis and proper treatment. This article provides an overview of these conditions, their pathophysiology, and diagnosis.