In this report, the case of a mixed-breed, female intact, eight-year- old dog, that was presented with a ten-day history of lethargy, anorexia, weight loss, occasional vomiting, coughing and sporadic dispnea is described; the clinical, radiographic and ultrasonographic findings suggested as the most likely diagnosis a lung lobe (right middle) torsion, which was confirmed by means of an exploratory thoracotomy; the therapy included resection of the affected lobe; no underlying etiology was identified. The patient recovered fully from the lobar torsion; however, two weeks after surgery the dog showed severe right forelimb lameness and the radiographic findings suggested a bone tumor in the proximal epiphysis of the humerus; the owners allowed only analgesic therapy and one month later the patient was euthanized due to a possible lung metastases; it is possible that the neoplasm and the metastases were concomitant events without a cause-effect relationship; however, there might also have been an association between a traumatic and stressing process (the lung torsion) with the development of an underlying oncologic process.