Toxic epidermal necrolysis (TEN) and Stevens–Johnson syndrome (SJS) are two terms that describe the clinical spectrum of a severe, life-threatening, blistering disorder of the skin and mucous membranes. Historically, more extensive skin loss (greater than 30% of body surface) is labeled TEN, whereas SJS is usually associated with less than 10% of body surface skin loss (see Chapter 16). In TEN/SJS, there is often a 1- to 3-day prodrome period of fever, conjunctivitis, pharyngitis, or pruritus. Frank skin pain and tenderness constitute an ominous sign. Mucosal surfaces of the mouth, eyes, genitalia, and anus are affected early in the disease (Fig. 31-1). Shortly thereafter, the patient develops widespread bullae that are easily ruptured; target lesions may also be seen (Fig. 31-2). The bullae can be extended laterally when pressed down upon, or the skin may tear when it is rubbed (Nikolsky’s sign). TEN/SJS may progress dramatically to sheets of skin loss (Fig. 31-3).