Background: Gianotti-Crosti syndrome (GCS) or infantile papular acrodermatitis presents as a symmetric erythematous lichenoid papular and papulovesicular eruption of the face, extremities, and buttocks, usually occurring in young children. GCS has been associated with hepatitis B and enteroviruses, as well as Epstein-Barr virus (EBV) and, rarely, cytomegalovirus. Objective: The purpose of this study was to use immunohistochemical studies to determine the pattern of the lymphoid infiltrate and evidence for viral antigens in cases of EBV-associated GCS. Methods: Routine histologic and immunohistochemical stains were evaluated in 3 patients with typical GCS. All 3 patients showed serologic evidence of an acute EBV infection. The immunohistochemical studies included monoclonal antibodies for CD3, CD4, CD8, CD20, TIA, S-100 protein, KP-1, EBV latent membrane antigen-1, and EBV-encoded nuclear antigen-2. Results: All biopsy specimens showed minimal epidermal spongiosis with marked papillary dermal edema. The associated inflammatory infiltrate showed a mixed mononuclear cell infiltrate with rare eosinophils. Immunohistochemical stains for latent membrane antigen-1 and EBV-encoded nuclear antigen-2 were negative for EBV. The majority of mononuclear cells showed membrane staining for CD3, 30% to 40% of the CD3 mononuclear cells showed positive staining for CD4, and 50% to 60% showed positive staining with CD8. TIA⁺ cells appeared to correspond to the CD8⁺ cells. Conclusion: Although papillary dermal edema has been reported within the spectrum of histologic findings in GCS, it was marked and a consistent finding in the 3 cases in which EBV was the most likely etiologic agent. The presence of large numbers of cytotoxic T cells in the inflammatory infiltrate may have accentuated this histologic finding and may be a relatively distinctive histologic finding with GCS associated with EBV. (J Am Acad Dermatol 2000;43:1076-9.)