Most violent behaviors arise from wakefulness. It is important to realize that violent behaviors that may have forensic science implications can arise from the sleep period. By virtue of the fact that these behaviors arise from sleep, they are executed without conscious awareness, and, therefore, without culpability. The most common underlying conditions arising from sleep are disorders of arousal (sleepwalking and sleep terrors), the rapid eye movement sleep behavior disorder, and nocturnal seizures. In addition, there are a number of psychiatric conditions (dissociative disorders, malingering, and Munchausen syndrome by proxy) that actually arise from periods of wakefulness occurring during the sleep period. The clinical and medico-legal evaluation of such cases is outlined, and should be performed by a multidisciplinary team of experienced sleep medicine practitioners.