A 4 year old, male castrated, domestic longhair presented to the Cornell Internal Medicine Service for a two month recheck following an acute renal failure (ARF) episode. During his previous visit two months prior he had presented to the Cornell Emergency Service with a complaint of listlessness, lethargy, and vomiting bile. Blood work revealed severe azotemia (BUN 242mg/dL, creatinine 30 mg/dL), hyperkalemia (8 mEq/L), hyperphosphatemia (12.8 mEq/L), and a high anion gap metabolic acidosis. An ECG exhibited tented T-waves and flattened P-waves consistent with hyperkalemia. An abdominal ultrasound revealed bilateral pyelectasia (more severe on the right), bilateral proximal hydroureters, and a very small bladder. On urinalysis, protein, white blood cells, and bacteria were observed, consistent with a urinary tract infection. He was medically managed overnight (IV fluids with dextrose, diuretics, calcium gluconate, insulin, and antibiotics) in an effort to correct electrolyte imbalances, stabilize his acid base abnormalities, and promote urine production. However medical management was unsuccessful in fully achieving any of these goals so the patient was transferred to another facility to receive hemodialysis the following morning. The patient’s azotemia improved greatly following several treatments of intermittent hemodialysis [BUN 37 mg/dL (ref 15-34), Creatinine 2.6 mg/dL (ref 0.8-2.3)]. A recheck ultrasound was performed and showed mild improvement in his left kidney characterized by improved renal pelvic dilation (improved from 2.2 cm on initial presentation down to 1.6 cm. His right kidney remained unchanged but given his clinical improvement, further diagnostics were not pursued. Although he continued to improve clinically, the etiology for his acute renal failure crisis remained unknown. The patient was discharged with baytril and subcutaneous fluids.