A 12 year old dog was submitted for a routine pregnancy examination. The information received from the owner was that the animal had been mated 45 days previously. During abdominal palpation, a hard, round mobile structure was detected. Extension of the tumour from the right ovary into the abdomen was determined by ultrasonography. Hemogram, blood biochemistry, estradiol and serum progesterone analyzes were performed before surgery. An ovariohysterectomy was performed and 1.6 L of ascites fluid aspirated. A tumour in the right ovary weighing 1.3 kg was detected. Histopathological examination revealed ovarian papillary cystadenoma. One month after the operation, the animal showed good general condition, however, five months after the operation, the state of health deteriorated. Euthanasia followed this, because the metastases were detected in the repeated laparotomy operation. As a result, Increased serum E2 and E2/ P4 ratio (3.15), and sonographically detectable abdominal mass and ascites could be useful for the dectection of the ovarian tumour in bitch. In case of rapidly growing papillary adenomas, frequent post-operative controls should be recommendable.