Lethal catatonia is one of catatonic spectrum, but it differentiates itself to a separate entity as a syndrome because of its severity and lethality. The prevalence of this disorder may have declined worldwide, coinciding with the advent of modern psychopharmacologic agents and other advances in medical treatment. The patient reported here was an 11-year old boy, showing catatonic excitement and stuporous condition with high fever, autonomic dysfunction and several catatonic symptoms. This is a case of successful treatment by using intensive medical monitoring and conservative treatment in an intensive care unit, combined with pharmacological treatment and electroconvulsive therapy during the early phase of lethal catatonia with mild symptoms.