Cyanide is a lethal poison that is widely available from many sources throughout the world. It has been used as a suicide and homicide agent throughout history and is a likely agent for terrorist attacks due to its chemical profile. Although rarely encountered, cyanide can be quickly fatal if not treated immediately with a cyanide antidote. Until recently, the only cyanide antidote available in the United States was the cyanide antidote kit, which has the risk of causing significant adverse effects in many patients. However, hydroxocobalamin (Cyanokit) was recently approved in the United States for the treatment of known or suspected cyanide toxicity. This article reviews cyanide toxicity and the place in therapy for hydroxocobalamin as a cyanide antidote.