Herpes associated erythema multiforme (HAEM) is an acute exudative dermatic and mucosal disease caused by infecting herpes simplex virus. It has recurrence and idiorestriction, characterized by increasing of CD4+T leukomonocyte. This article reports a case of herpes associated erythema multiforme, and by way of reviewing relevant literature, discusses the possible mechanism, diagnosis, treatment and prognosis of HAEM.