In acquired ichthyosis related to HTLV-I-associated myelopathy, histopathology revealed orthokeratotic hyperkeratosis and a perivascular inflammatory infiltrate of mononuclear lymphocytes, with areas of parakeratosis and foci of epidermotropism in rare cases. The expression profiles of K1, K10 and involucrin were similar to those in normal skin. The diffuse coexpression of K16 with K1 and K10 throughout the analysed epidermis, as well as the occurrence of restricted areas of parakeratosis expressing K6, indicate the presence of keratinocyte activation with induction of the alternative keratinization pathway, probably dependent on the cytokines liberated by the mononuclear cells of the dermal inflammatory infiltrate infected with HTLV-I. The absence of acanthosis and of increased cellular kinetics, as shown by the low rate of Ki-67 antigen expression, allow the inference that the pattern of acquired ichthyosis related to HTLV-I-associated myelopathy may be retentional. The observation of foci of parakeratosis expressing K6 in three specimens suggests that, at least in certain areas and in some cases, interference with epidermal differentiation and maturation occurs.