A case of pagetoid reticulosis is presented. Histopathology showed infiltration of the epidermis by mononuclear cells. Twenty percent of the mononuclear cells showed the presence of lysozyme indicating a histiocytic origin. Electron microscopy confirmed the presence of lymphocytes and histiocytes but these cells were outnumbered by Sézary cells. The presence of large numbers of Sézary cells indicates that pagetoid reticulosis is a cutaneous T-cell lymphoma closely related to mycosis fungoides.