The clinical spectrum of MM is variable. Infiltration of bone and bone marrow by malignant plasma cells results in severe osteopenia, lytic lesions, pathological fractures and anaemia. Occasionally, significant numbers of plasma cells circulate in the bloodstream. Hypercalcaemia and Bence Jones proteinuria are the main reasons for renal impairment, but amyloidosis and monoclonal immunoglobulin deposition should also be considered. Neurological impairment is most often due to spinal cord pressure by an extradural plasma cell tumour. In some patients, symptoms and signs of peripheral neuropathy may be present. Amyloidosis complicates the course of a minority of patients with MM and further impairs the performance of affected patients. Circulating monoclonal protein may increase serum viscosity, impair the function of platelets and coagulation factors, and behave as a cryoglobulin. The levels of uninvolved immunoglobulins are usually decreased, rendering patients susceptible to various bacterial infections. One or more of these complications provides a clue for the diagnosis, forms the basis for defining prognosis and must be managed expeditiously and concurrently, with the institution of specific treatment for the myeloma.