A case of acute febrile neutrophilic dermatosis (Sweet's syndrome) associated with Behçet's disease occurring in a 48 year old woman is reported. She fulfilled the diagnostic criteria for both Sweet's syndrome and Behçet's disease. There have been several reports of this association. Herpes simplex virus was isolated from a genital ulcer in our patient. The possible role of herpes simplex virus in this interesting association of Behçet's disease and Sweet's syndrome is discussed and a review of the literature is made.