Toxic epidermal necrolysis is perhaps the most formidable disease encountered by dermatologists. Uncommon but not rare, toxic epidermal necrolysis occurs in 60 to 70 persons per year in France. It remains as puzzling a disorder as it was 34 years ago, when described by Lyell. Whether or not toxic epidermal necrolysis is the most severe form of erythema multiforme is still the subject of discussion. The physiopathologic events that lead to this rapidly extensive necrosis of the epidermis are not understood. Indirect evidence suggests a hypersensitivity reaction, but the search for potential immunologic mechanisms has resulted in little data to support this hypothesis. Accumulated clinical evidence points to drugs as the most important, if not the only, cause of toxic epidermal necrolysis. Sulfonamides, especially long-acting forms, anticonvulsants, nonsteroidal anti-inflammatory agents, and certain antibiotics are associated with most cases of toxic epidermal necrolysis. Many other drugs have been implicated in isolated case reports. All organs may be involved either by the same process of destruction of the epithelium as observed in the epidermis or by the same systemic consequences of "acute skin failure" as seen in patients with widespread burns. Sepsis is the most important complication and cause of death. Approximately 20% to 30% of all patients with toxic epidermal necrolysis die. Elderly patients and patients with extensive lesions have a higher mortality rate. Surviving patients completely heal in 3 to 4 weeks, but up to 50% will have residual, potentially disabling ocular lesions. The prognosis is improved by adequate therapy, as provided in burn units, that is, aggressive fluid replacement, nutritional support, and a coherent antibacterial policy. Corticosteroids, advocated by some in high doses to halt the "hypersensitivity" process, have been shown in several studies to be detrimental and should be avoided.