A 35-year-old man suffered simultaneously from nodular sclerosis Hodgkin's disease (HD), Langerhans' cell histiocytosis and multiple myeloma (MM). There was no prior history of irradiation or chemotherapy, and clinically the lymphoma was confined to cervical lymph nodes. Immunohistochemically, neoplastic lymphoma cells reacted with CD15 and CD30 markers. The patient's bone marrow exhibited a diffuse infiltration by rather atypical plasma cells showing kappa immunoglobulin light-chain restriction. At 14 months after the diagnosis, after autologous bone marrow transplantation, the clinical evolution is favourable with complete remission of the diseases. This is the first time that the coexistence of these three haematological disorders has been discussed, and only the fourth documented case of simultaneous HD and MM. Speculations about the significance of this finding are discussed.