One year after the onset of chronic lymphocytic leukemia, an elderly man had scaly cutaneous plaques on the thighs that clinically and histologically resembled the mycosis fungoides type of cutaneous T-cell lymphoma. Two years later the patient had indurated, red dermal nodules on the face that clinically and histologically were characteristic of cutaneous chronic lymphocytic leukemia. Immunophenotyping results from a facial nodule confirmed the presence of a B-cell infiltrate (CD20+). Immunophenotyping of a lesion on the right thigh showed that half the cells were composed of a CD2+, CD45RO+ (UCHL-1+) upper dermal and focally epidermotropic population of T cells consistent with mycosis fungoides; however, these T cells coexisted with an equal number of CD20+ B cells arranged in distinct clusters. DNA from the thigh lesion exhibited a B-cell immunoglobulin gene rearrangement, but the T-cell receptor gene rearrangements were germline. In this case, the evidence favors a mycosis fungoides simulant occurring as a reactive T-cell infiltrate to an underlying B-cell chronic lymphocytic leukemia.