Round atelectasis (RA) is an uncommon entity occasionally encountered in daily practice. The pathogenesis of RA has not been clarified. It is characterized by the invagination of fibrotic visceral pleura into the mass. The clinical importance of this benign malady resides in its resemblance to pulmonary malignancy on the chest radiograph and CT scan. Not well recognized, RA may be easily mistaken as lung cancer, thus leading to unnecessary surgical intervention. Chest sonography, a new modality for chest disease diagnosis, is an available, ideal, and accurate diagnostic tool for peripheral pulmonary lesions such as RA. Herein, we present a case of RA with its characteristic sonographic findings.