A 2-year-old female Labrador retriever was presented with anorexia and abdominal distention. Laparotomy revealed the presence of a 31-cm ovoid mass in the portion of the left ovary and an 11-cm round mass in the left retroperitoneal region. Both masses were surgically removed. Histopathological examination of the masses revealed a mixture of tissues characteristic of teratomas, such as multiple bronchial and intestinal cysts, hair follicles, sebaceous and apocrine sweat glands, and neuron tissue with intervening cartilage, bone and fat tissue. This paper appears to be the first report of primary retroperitoneal teratoma in the dog.