A 20-year-old cow was presented due to chronic diarrhea and weight loss. The clinical examination revealed a markedly enlarged left ovary. However, a cause of the diarrhea could not observe. The examination of the feces was negative for a parasites or bacteria causing diarrhea. The results of hematological and biochemical analyses revealed a mild leucocytosis, bilirubinaemia, higher activities of the enzymes aspartate transaminase, gamma-glutamyltransferase and creatine kinase. The plasma concentrations of estrogen and testosterone were below the detection limits, progesterone concentration was 2.7 ng/ml. The postmortem examination revealed a bile ductule carcinoma with metastases in the lung and in lung and mestenterial lymph nodes. The cause of the tumor remained unclear. Diarrhea might have been the consequence of a portal hypertension due to the tumor. The pathological examination confirmed the clinical diagnosis of the ovarian tumor. The genesis of the ovarian tumor may be independent of the genesis of the bile ductule carcinoma.