A young adult (approximately 20 months), 125 g, female degu (Octodon degus) was housed with a male degu for approximately 1.2 years as a breeding pair. The female was multiparous and had weaned its third litter 2 weeks earlier. The degu was reported to the veterinary service for bloody vaginal discharge and a hunched, thin appearance of 1 day's duration. On physical examination, it exhibited cachexia, molting, slight matting of the hair around the eyes, and moderate dehydration. Hematology results included anemia and leukopenia with lymphocytopenia. Biochemical abnormalities included severe azotemia and phosphatemia. Urine specific gravity was 1.016. The condition of this animal prohibited its continued use in the breeding colony, so it was submitted for necropsy. On gross examination, the left kidney measured 10 × 15 mm, had an irregular surface, and was pale and mildly enlarged, consistent with compensatory hypertrophy. The right kidney was small (5 × 8 mm) and cystic. Both adrenal glands appeared mildly enlarged. Histologically, the left kidney had multiple regions with chronic, diffuse interstitial nephritis, and the right kidney was polycystic. There was mild, focal, cortical nodular hyperplasia in the adrenal glands. In the uterus, there was unilateral, locally extensive necrosis of the endometrium. The clinical chemistry results and histopathology findings are supportive of a diagnosis of renal failure secondary to chronic nephritis and polycystic kidney disease. The etiology of the nephritis is unknown. Polycystic kidney disease can be congenital or hereditary in other rodents.