A seven-month-old male alpaca (Lama pacos) with signs of abdominal straining was examined. A fluid-filled structure was palpable in the mid-abdominal region, and ultrasonography revealed a hydronephrosis of the right kidney, with an associated mega-ureter. The affected kidney was removed and the clinical signs resolved. Histological examination of the kidney revealed the unusual congenital abnormality of ureteral duplication. It is suggested that the hydronephrosis developed as a result of this underlying condition.