Primary Plasma cell leukaemia (pPCL) is a rare plasma cell (PC) malignancy. The strict criteria for the diagnosis is an absolute PC number greater 2 X 10⁹/L or a plasmocytosis accounting for > 20% of the differential white cell count that does not arise from a pre-existing multiple myeloma. pPCL was associated with aggressive clinic-biological features. Primary Plasma cell leukaemia is more characterised by an extra medullar involvement such as hepatomegaly, splenomegaly, lymphadenopathy, lepto-meningeal infiltration or extramedullary plasmocytomas. The prognosis of pPCL is very poor. We report the case of a fifty eight year-old man directed to the haematology department for diagnosis of pPCL revealed by a thoracic plasmocytomas mimicking a thoracic neoplasm. The patient received chemotherapy including a classic treatment for multiple myeloma but developed a pulmonary embolism. This case illustrates an uncommon presentation of pPCL the difficulty treating by multiple myeloma chemotherapy.