A 2-year-old, male castrated Cane Corso, was presented to Cornell University Hospital for Animals for further evaluation of frank red urine of 2.5 weeks duration and recent stranguria and inappetance. The dog was initially treated by his primary care veterinarian with antibiotics for a presumptive urinary tract infection, with only transient resolution of his signs. On presentation, the dog was bright, alert, responsive, and had vital parameters within normal limits. His caudal abdomen was mildly painful on palpation. A complete blood cell count, biochemistry panel, disseminated intravascular coagulation panel, von Willebrand factor immunoassay, urinalysis, and urine culture and susceptibility were performed, revealing a mild regenerative anemia, borderline hypoproteinemia, and macroscopic hematuria. No calculi were seen on abdominal radiographs. Ultrasound showed a large intraluminal thrombus in the urinary bladder and a mildly dilated left ureter. The right ureter and both renal pelves appeared normal. Cystoscopy revealed hemorrhage from one ureter, but the large bladder thrombus impeded visualization of the second ureter. Idiopathic renal hematuria, a rare condition in which hemorrhage from one or both kidneys occurs without an obvious cause, was the top differential diagnosis. Treatment options were thoroughly discussed and a renal-sparing treatment was highly recommended, but the dog's owners elected an abdominal exploratory surgery with nephrectomy if bleeding was found to be unilateral. At surgery, both ureters were catheterized and mild hematuria was present on the right side with no detectable abnormalities on the left. A right nephroureterectomy was performed and the tissues were submitted for histopathology with no significant abnormalities reported. The dog recovered well in the immediate post-operative period, but two days later developed severe hematuria, stranguria, and formed another large thrombus in the urinary bladder. The dog was euthanized and necropsy revealed severe hemorrhage and distention of the left renal pelvis as well as intraluminal hemorrhage and distention of the left ureter, supporting a diagnosis of bilateral idiopathic renal hematuria.