A case of ovine pulmonary adenocarcinoma is reported in a five month-old indigenous lamb of the department of Puno, Peru. At clinical inspection, the animal presented dyspnea, body weight loss and abundant lung secretion. The necropsy revealed in both diaphragmatic lobes the presence of two grayish white nodular formations with plenty of white foamy fluid emanating from the trachea. At the cut surface of the tumor was observed irregular micronodules with a tendency to coalesce. Histologically, the tumors were composed of columnar or cuboidal cells isolated by a fibrotic stroma and surrounded by alveoli flooded with macrophages of vacuolar cytoplasm. Intraluminal polyps were observed in the terminal bronchioles compromising the bronchiolar epithelium. Molecular analysis of lung tissue and fluid contained the exogenous genetic sequences of type D retrovirus. Retroviral infection with multi nodular presence of neoplastic lesions in a lamb corroborates the susceptibility of indigenous Andean sheep to retroviral infection.