Hamartomas are nonmalignant masses of normal tissue organized in a chaotic manner. Here, we describe a 6-month-old 120 kg Chilean Criollo foal that manifested chronic hematuria observed since birth. Severe anemia and lack of development were the main complaints of this referral. The foal was depressed and in poor body condition, and had lagged development and a coarse haircoat. Mucous membranes were pale, and numerous blood clots were observed toward the end of micturition. Severe normocytic normochromic anemia was confirmed by hematological analysis; there were no significant findings in serum biochemistry or coagulation tests. Transabdominal ultrasonography and urinary tract endoscopy yielded no clinically relevant results. Empirical treatment was initiated on a tentative diagnosis of idiopathic renal hematuria (dexamethasone 0.1 mg/kg [0.045 mg/lb], q 24 hours, IV, sodium ceftiofur 2.2 mg/kg [0.99 mg/lb], IM, q 24 hours, and blood transfusions), but the foal's condition further deteriorated, warranting euthanasia. Necropsy revealed a vascular malformation on the extraluminal portion of the proximal urethra at the bladder junction, with a 3 mm urethral communication. Histopathologic examination confirmed this mass to be a hamartoma of vascular origin, which incidentally communicated with the urethral lumen and led to progressive blood loss. In this case, the location of this malformation impeded its discovery and ultimately an accurate diagnosis. Hamartomas are currently not listed as a differential diagnosis for bleeding-related urinary tract disorders in the modern literature; therefore, we propose that they should be considered as a differential diagnosis in cases of unexplained or refractory idiopathic hematuria.