Pigmentary changes in mycosis fungoides usually occur in association with poikiloderma atrophicans vasculare or following therapy and regression of lesions. Several cases of hypopigmented mycosis fungoides have also been reported. We present the case report of a patient who developed pruritic, diffuse macular hyperpigmentation of the skin. Biopsy specimens from hyperpigmented skin revealed histologic and ultrastructural features typical of mycosis fungoides. Giant melanin granules were found in the tumor cells, as well as in keratinocytes and Langerhans cells. As far as we know, this is the first report of cutaneous hyperpigmentation as a single presenting sign of mycosis fungoides.