Plasma cell leukemia (PCL) represents the most aggressive form of monoclonal gammopathy for which new treatment approaches are needed. Here we report the effect of Bortezomib on cells from 4 patients with PCL, as well as the in vivo efficacy on a patient with secondary PCL. Bortezomib reduced PCL numbers and was more efficient in cell growth inhibition than dexamethasone or doxorubicin. Treatment with Bortezomib induced procaspase-3 and poly(ADP-ribose) polymerase cleavage and decreased the amount of extracellular signal regulated kinase (Erk1/2) and phospho-Erk1/2. However, Bortezomib did not substantially affect the levels of the Erk1/2 upstream activating kinase (MEK1), p27 or p21. Finally, we had the opportunity to use Bortezomib in a heavily pretreated patient with overt secondary PCL and severe anemia and thrombocytopenia. Following Bortezomib treatment, circulating plasma cells disappeared; what is more striking, the peripheral blood counts returned to normal, becoming transfusion-independent. These data support the inclusion of Bortezomib in the therapeutic armamentarium of PCL.