CASE DESCRIPTION A 6-year-old neutered male domestic shorthair cat was evaluated because of signs of abdominal pain and anuria of 12 hours' duration after vehicular trauma. CLINICAL FINDINGS Lethargy, mydriasis, bradycardia, abdominal distension, and signs of pain on abdominal palpation were observed. Abdominal ultrasonography revealed moderate urinary bladder distension without evidence of free abdominal fluid; hematologic evaluation revealed leukocytosis with high BUN and serum creatinine concentrations. TREATMENT AND OUTCOME The patient was hospitalized, medical stabilization was attempted, and an indwelling urinary catheter was placed. Urinary output was < 1 mL/kg/h (< 0.45 mL/lb/h), and signs of abdominal pain persisted despite treatment. The next day, ultrasonographic examination revealed fluid in the retroperitoneal space, and ureteral rupture was suspected. Exploratory laparotomy confirmed retroperitoneal fluid accumulation; a large hematoma surrounded the right kidney and perirenal structures. An abdominal drain was placed to aid patient stabilization. Three days later, IV pyelography revealed rupture of the proximal part of the right ureter. Ureteroneocystostomy was performed with elongated cystoplasty through a Boari flap and caudal transposition of the right kidney (renal descensus). On follow-up examination 18 months after treatment, the cat was free of clinical signs, and results of ultrasonography, CBC, and serum biochemical analysis were unremarkable. CLINICAL RELEVANCE Results suggested that a Boari flap procedure with renal descensus could be a feasible alternative in the management of proximal ureteral rupture in cats, but research is needed in this area.