A newborn male Romagnola calf, who had died a few hours after birth, was submitted for postmortem examination. Necropsy revealed a 23 cm × 22 cm × 5 cm, pale pink, lobulated, elastic, partially fluctuant mass that protruded from the dorsal retroperitoneal space into the abdominal cavity, extending from the diaphragm to the left kidney. The mass consisted of mature pulmonary tissue and was consistent with a pulmonary choristoma. The gross and microscopic appearance of this rare tumor-like congenital lesion and the possible pathogenesis are discussed.