The treatment of choice for solitary plasmacytoma is radiation therapy. The local response rate exceeds 90%. Solitary plasmacytoma is characterized by the neoplastic proliferation of a single clone of plasma cells involving invasion of skeletal structures or extramedullary soft tissues. Progression to multiple myeloma is more common in solitary plasmacytoma of the bone than in extramedullary plasmacytoma. In the treatment of multiple myeloma radiotherapy is effective in palliating local symptoms, such as painful bone metastases, radiculopathy and spinal cord compression. Long-course radiotherapy (10×3 Gy, 20×2 Gy) results in better outcome of pain relief, recalcification rates and local control rates. Patients with a poor survival prognosis benefit from short-course radiotherapy (1×8 Gy, 4×5 Gy). Total body radiation as part of conditioning protocols prior to autologous blood stem cell transplantation is no longer a treatment of choice.