Background A subset of subjects with atopic dermatitis (AD) are susceptible to serious infections with herpes simplex virus, called eczema herpeticum, or vaccina virus, called eczema vaccinatum. Objective This National Institute of Allergy and Infectious Diseases–funded multicenter study was performed to establish a database of clinical information and biologic samples on subjects with AD with and without a history of eczema herpeticum (ADEH+ and ADEH− subjects, respectively) and healthy control subjects. Careful phenotyping of AD subsets might suggest mechanisms responsible for disseminated viral infections and help identify at-risk individuals. Methods We analyzed the data from 901 subjects (ADEH+ subjects, n = 134; ADEH− subjects, n = 419; healthy control subjects, n = 348) enrolled between May 11, 2006, and September 16, 2008, at 7 US medical centers. Results ADEH+ subjects had more severe disease based on scoring systems (Eczema Area and Severity Index and Rajka-Langeland score), body surface area affected, and biomarkers (circulating eosinophil counts and serum IgE, thymus and activation-regulated chemokine, and cutaneous T cell–attracting chemokine) than ADEH− subjects ( P < .001). ADEH+ subjects were also more likely to have a history of food allergy (69% vs 40%, P < .001) or asthma (64% vs 44%, P < .001) and were more commonly sensitized to many common allergens ( P < .001). Cutaneous infections with Staphylococcus aureus or molluscum contagiosum virus were more common in ADEH+ subjects (78% and 8%, respectively) than in ADEH− subjects (29% and 2%, respectively; P < .001). Conclusion Subjects with AD in whom eczema herpeticum develops have more severe TH 2-polarized disease with greater allergen sensitization and more commonly have a history of food allergy, asthma, or both. They are also much more likely to experience cutaneous infections with S aureus or molluscum contagiosum.