Parasomnias are undesirable behavioral or experiential phenomena arising from the sleep period. Once felt to be a unitary phenomenon, it is now clear that a wide variety of sleep disorders are capable of resulting in complex behaviors arising during sleep. The most common are disorders of arousal and rapid eye movement sleep disorder. Less common conditions include nocturnal seizures and psychogenic dissociative states. Malingering and Munchausen syndrome by proxy, while they are not actually parasomnias, may masquerade as parasomnias. Careful clinical and sleep laboratory evaluation can usually provide an accurate diagnosis with effective therapeutic implications. Due to the potential forensic implications, sleep medicine specialists may be asked to participate in legal proceedings resulting from sleep-related violence. An awareness of the spectrum of such behaviors, and their clinical and legal evaluation, is becoming more important in the practice of sleep medicine.