Infective dermatitis associated with HTLV-I (IDH) is a chronic, recurrent, exudative eczema occurring in childhood which is considered to be a risk factor for the development of lymphoma and HTLV-I-associated myelopathy/tropical spastic paraparesis. Skin biopsies from 19 patients with IDH were studied histologically and immunohistochemically using the following antibodies: anti-CD3, CD45RO, CD20, CD79a, CD4, CD8, CD56, CD57, TIA-1, granzyme-B, and perforin.A chronic dermatitis similar to atopic and seborrheic dermatitis was observed in 15 cases, whereas architectural aspects mimicking mycosis fungoides were observed in the remaining four. The infiltrate consisted predominantly of CD8+ lymphocytes and of CD57+ cells in the dermis and epidermis. TIA-1 and granzyme-B were expressed in 15/18 cases and 5/19 cases at the proportion of ≤ 15% and ≤ 3%, respectively. All cases were negative for perforin and CD56. Like other dermatites, histologically IDH may represent a benign simulator of mycosis fungoides. IDH shows a predominance of CD8+ cells and a low percentage of cells with cytotoxic granules, indicating that most CD8+ lymphocytes are not activated. These findings differ from the immunohistochemical pattern of atopic and seborrheic dermatitis, possibly representing additional means of differentiation between IDH and these dermatites. The distribution of CD57+ cells suggests that they play a role in the inflammatory process.