The histologic features of an epidermotropic cutaneous lymphoma in a dog are presented. The neoplasm, which was intensely epidermotropic, thoroughly invaded the follicular and apocrine gland epithelium. The intense epidermotropism was retained in the tumor stage. By comparison to human mycosis fungoides, the cell nucleus was less convoluted and the infiltrate was less polymorphic. The lymphoid cell appeared to undergo neoplastic transformation into a cell with a large pale nucleus, often with a prominent nucleolus and variable cytoplasm. In situ marker studies are needed to clarify the cell type in this neoplasm. These studies could have relevance for the pathogenesis of human epidermotropic lymphoma.