A 1.5-year-old, female, entire German shepherd dog was presented for evaluation of an abdominal mass. The dog had a 4-month history of polydipsia, polyuria, diarrhoea, and weight loss despite polyphagia. Abdominal ultrasound confirmed a large abdominal mass suspected to be uterine in origin. An exploratory celiotomy revealed a 4.3 kg, 26 × 17 × 17 cm multinodular mass entirely encompassing the uterus, left ovary and left kidney. A combined ovariohysterectomy and left nephrectomy were undertaken. Histopathology confirmed stage ΙΙ renal nephroblastoma with favourable histology. Chemotherapy was declined and 86 days following surgery, significant abdominal metastases were identified on a computed tomography scan. The patient was euthanased 113 days after surgery due to progressive disease. This is the first report to display the rapid presumed metastasis of a canine nephroblastoma, without gross metastasis at initial surgical resection, through advanced imaging. This is also the first reported case of polyphagia despite weight loss as a presenting clinical sign.