The early recognition of ifosfamide-related renal dysfunction, including arginine vasopressin resistance (previously referred to as diabetes insipidus), which is characterized by polyuria due to the inability of the collecting duct to concentrate urine, as well as direct proximal tubular injury, which is characterized by numerous metabolic disturbances including hypophosphatemia, metabolic acidosis, hypokalemia, and glucosuria, is paramount to timely initiation of treatment and titration of desmopressin. This evidence concerns the gene AVP and hypophosphatemia.