Lichen striatus (LS) is an uncommon dermatosis that generally affects children. The histopathology of LS often shows a polymorphic epidermal reaction process of variable lichenoid and spongiotic changes having no specific histopathological criteria or simulating other diseases. In the present study, we have evaluated the histopathological features of 41 biopsy specimens and the immunohistochemical aspects of 10 cases of LS. In 50% of the cases, we found histopathological and immunopathological features constantly present and allowing a correct diagnosis. In 9 cases, the histopathology was not specific, and in 10 cases, a clear differentiation from other diseases was not possible. Immunohistochemical study demonstrated a CD3+ T-lymphocytic infiltration in which CD8+ cells surrounded necrotic keratinocytes and intraepidermal vesicles filled with Langerhans cells. These findings seem to corroborate the hypothesis that a somatic mutation of a keratinocytic clone could induce an autoimmune response of the host.