Parasomnias are unpleasant or undesirable behavioral or experiential phenomena that occur predominately or exclusively during sleep. These phenomena were initially thought to represent a unitary event, often attributed to psychiatric disease. Recent clinical and polygraphic analysis has revealed that they are, in fact, the result of a large number of very different conditions, most of which are diagnosable and treatable. In fact, most are not the manifestation of psychiatric disorders, and they are far more prevalent than previously suspected. Although there are many parasomnias (1,2), from a practical standpoint only the few that comprise the overwhelming majority will be discussed in this review. These include disorders of arousal, rapid-eye-movement sleep behavior disorder, nocturnal seizures, and restless legs syndrome. Most parasomnias are readily diagnosable and, more importantly, are treatable.