Erythema multiforme (EM) is an acute inflammatory disease of the skin and mucous membranes that causes a variety of skin lesions—
hence the name “multiforme.” The oral lesions, typically inflammation accompanied by rapidly rupturing vesicles and bullae, are often an important component of the clinical picture and are occasionally the only component. Erythema multiforme may occur once or recur, and it should be considered in the diagnosis of multiple acute oral ulcers whether or not there is a history of similar lesions. There is also a rare chronic form of EM. EM has several clinical presentations: a milder self-limiting form and severe life-threatening forms that may present as either Stevens-Johnson syndrome or toxic epidermal necrolysis (TEN).