The coexistence of two non-Hodgkin lymphomas in one patient is extremely rare. We describe a patient who suffered for 17 years from chronic lymphocytic leukemia of B-cell origin with bone marrow and peripheral blood involvement until he developed clinically typical mycosis fungoides of the skin. The neoplastic lymphatic cells in the skin infiltrates were T-cells of the helper/inducer phenotype and thus differed morphologically and by immunological markers from the neoplastic cells in peripheral blood and bone marrow. The clonal B-cell expansion was controlled well over many years by cytotoxic drug therapy, the cutaneous T-cell lymphoma only with limited success by oral photochemotherapy owing to lack of compliance. The patient died 3 years after the diagnosis of MF from a parallel exacerbation of both diseases. Extensive immunohistochemical studies verified the nature of both lymphomas in vivo and at autopsy.