Stevens-Johnson syndrome (SJS) is a life-threatening condition affecting the skin in which cell death causes the epidermis to separate from the dermis. The syndrome is thought to be a hypersensitivity complex affecting the skin and the mucous membranes. Although the majority of cases are idiopathic, the main class of known causes is medications, followed by infections and (rarely) cancers.

There is agreement in the medical literature that Stevens-Johnson syndrome can be considered a milder form of toxic epidermal necrolysis (TEN). However, there is debate whether it falls on a spectrum of disease that includes erythema multiforme and erythema multiforme major (also known as erythema multiforme majus).

SJS is a rare condition, with a reported incidence of around one case per million people per year. In the United States, there are about 300 new diagnoses per year.