Bronchopulmonary sequestration is a congenital abnormality of nonfunctional pulmonary tissue that lacks normal connections with the bronchial tree. The sequestered tissue typically receives the majority of its blood supply from systemic vessels, most often the distal thoracic or upper abdominal aorta. These lesions often are associated with fetal hydrops, polyhydramnios, and persistent masses postnatally. Bronchopulmonary sequestrations are thought to require resection owing to their predisposition for chronic pulmonary infections later in life. However, spontaneous in utero resolution of these lesions can occur. This report describes the real time, color Doppler, and duplex Doppler ultrasonographic investigation of an intrathoracic bronchopulmonary sequestration that resolved spontaneously. Our investigation of this case provides new insight into a possible mechanism for spontaneous regression of bronchopulmonary sequestration.