Cantharidin, or Spanish fly, is a lipid soluble irritant extracted from the blister beetle. Manifestations of cantharidin poisoning range from local vesiculobullous formation to gross hematuria, myocardial damage, denudation of the gastrointestinal tract, and occasionally death. Despite the wide spectrum of clinical symptomatology, the available information on this subject is extremely scanty. We have attempted the first review of this subject in this century. Currently cantharidin is the active ingredient in various wart removal compounds. The blister beetle has a ubiquitous distribution, with many species found in the southeastern United States. Although most case reports concern adults, the potential for pediatric poisoning is great. Treatment is primarily supportive.