A 69-year-old male patient was diagnosed with right-sided renal cell carcinoma and humoral hypercalcemia of malignancy caused by an excessive production of parathyroid hormone-related protein. The hypercalcemia led to acute tubular necrosis, so the patient had to be put on hemodialysis. The renal failure was accompanied by hyponatremic encephalopathy. Rapid correction of the hyponatremia might have initiated central pontine myelinolysis.