To examine whether there is a relationship between serum cholesterol level and sleep-related violence, we evaluated 15 patients with violent behavior during sleep (VBS) and 15 normal control subjects. The patient and control groups were matched for sex, age, and weight. There were 13 women and two men in each group. The patients with VBS had lower serum total cholesterol, triglyceride, and low-density lipoprotein levels than the healthy subjects. Low cholesterol may effect serotonergic neuronal activity and some types of 5-HT receptors, then may be related to violent behavior during sleep.