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A 6-year-old sexually intact male Yorkshire Terrier was evaluated because of a nonproductive cough and dyspnea of 10 days’ duration. The dog had been treated with amoxicillin-clavulanic acid and betamethasone without apparent improvement. Three days before evaluation, the dog became anorectic and had signs of depression. On physical examination, the dog had labored breathing and was tachypneic. Abnormalities detected on CBC and microscopic examination of a blood smear included a stress leukogram (leukocytosis, mature neutrophilia, and lymphopenia), poikilocytosis, and activated monocytes. The serum glucose concentration was 65.7 mg/dL (reference range, 80 to 120 mg/dL). Radiographs of the thorax were obtainedUltrasonography of the thorax revealed a moderate amount of slightly echoic pleural fluid. The right middle lung lobe was large with a globular appearance and was hypoechoic at the periphery; a small, centrally located area of clustered, reverberating foci consistent with gas was also visible (Figure 3). The bronchi were filled with fluid. Blood flow was not detected via color-flow, power, or spectral Doppler ultrasonography. The ventral portions of adjacent lung lobes were atelectatic; in those lung lobes, Doppler ultrasonography permitted detection of venous blood flow. The most likely differential diagnoses included torsion of the right middle lung lobe or abscess formation with secondary pleuritis. Trauma or neoplasia-induced consolidation of the right middle lung lobe and secondary pleural effusion were considered as less likely differential diagnoses. Torsion of the right middle lung lobe was confirmed during thoracotomy, and a lobectomy was performed. The dog recovered from surgery and anesthesia without complications. Lung lobe torsion is an uncommon condition characterized by rotation of a lung lobe around its axis; torsion usually occurs at the level of or in close proximity to the hilus. It causes vascular compromise leading to congestion, edema, and possibly hemorrhage and necrosis.1 Most cases of lung lobe torsion involve large, deepchested dogs (especially Afghan Hounds); however, the condition has been reported in several breeds including small, chondrodystrophic (especially Pugs) and toybreed dogs.2 Most commonly, the right middle (especially in deep-chested dogs and large-breed dogs with an intermediate conformation of the thorax) and left cranial lung lobe (especially in small, chondrodystrophic dogs) are affected.2 Rarely, multiple lung lobes can be affected.1 The most common radiographic signs are pleural effusion and increased opacity in the area of the affected lung lobe.1,3 Pleural effusion is usually bilateral (often asymmetric), but it can also be unilateral. The increased opacity (associated with loss of visualization of lobar vasculature) can be uniform or inhomogeneous because of the presence of gas in the affected lobe. Gas bubbles may be scattered throughout the affected lobe (vesicular lung pattern) or clustered in some portions.1 On ultrasonography, the affected lung lobe is usually large and hypoechoic; in most cases, centrally located, reverberating foci consistent with gas can be seen. In the dog reported here, gas clustered in the central portion of the affected lung lobe, detected during ultrasonography, was not detected on thoracic radiographs. The treatment of choice is surgical removal of the affected lobe, which results in an uncomplicated recovery in approximately 50% of dogs.2 Toy-breed dogs appear to have a better prognosis than large-breed dogs.