An infant suffered from psoriasiform dermatitis complicated by severe constitutional symptoms. During his 12 months of hospitalization, the symptoms exacerbated periodically despite numerous therapeutic trials. Histologic findings revealed lichenoid psoriasiform dermatitis with striking eosinophilic necrosis of epidermal cells and satellite cell necrosis. Immunohistochemically, CD1+ Langerhans cells had almost disappeared, and CD8+ cytotoxic-suppressor T cells were predominant over CD4+ helper-inducer T cells in the epidermis. These findings in the skin biopsy specimens suggested some similarity to graft-versus-host disease but no known cause of that disorder was proved. Finally, methotrexate was effective. The patient became afebrile, and his skin lesions improved, leaving almost no scarring. This patient seems to have had specific clinical features that do not correspond with any of the known dermatitis. Clinical, histologic, and laboratory findings did not uncover any etiologic factors.