The spectrum of neurologic complications of multiple myeloma (MM) and related conditions is as diverse as the conditions themselves. Complications range from direct compression (radiculopathy, spinal cord compression, base-of-the-skull tumor) to the infiltrative (amyloid, peripheral neuropathies, and numb chin syndrome of myeloma), the metabolic (slowed mentation from hyperviscosity, hypercalcemia, or uremia), and to autoimmune or cytokine-mediated (peripheral neuropathy). The two most common presentations are the compressive radiculopathy one sees in multiple myeloma and the peripheral neuropathies associated with many of the other disorders. The authors will review the neurologic complications of MM, monoclonal gammopathy of undetermined significance (MGUS), Waldenström macroglobulinemia (WM), POEMS syndrome, amyloidosis, and cryoglobulinemia.