Patients with malignancies frequently experience multiple electrolyte disturbances. In multiple myeloma, hypercalcemia and hyperphosphatemia are one of the most common metabolic disturbances observed as part of pathogenesis of the disease. However, in rare occasions and during the course of the disease, many patients can develop hypophosphatemia due to multiple factors that affects the phosphate absorption and excretion. We hereby present a 56 y/o woman recently diagnosed with multiple myeloma who developed severe hypophosphatemia during medical treatment. We should note that the following manuscript was presented at the 2019 American Association of Clinical Endocrinologists (AACE) 28th Annual Scientific and Clinical Congress.