This paper reports a case of congenital hydronephrosis and hydroureter in a dog. One canine was seen presenting difficulty in walking and abdominal enlargement. After treatment, there was no improvement. On reassessment, x-ray and ultrasound examinations revealed an unidentified increase in volume in the abdomen, and exploratory laparotomy was indicated. Unilateral congenital hydronephrosis was diagnosed in the left kidney and hydroureter with stenosis in the distal third and adherence to the left uterine horn, and an ovariosalpingohysterectomy was performed during the ureteronephrectomy. One month later, the patient presented decreased abdominal volume and locomotion without difficulties. Hydronephrosis and hydroureter are chronic changes that can cause irreversible organ damage.