Background <p>Extralobar pulmonary sequestration is a rare disease and is frequently associated with congenital malformations. Herein, we report an adult case of an unusual extralobar sequestration accompanied by a bronchogenic cyst and the concurrent absence of the left pericardium. </p> Case presentation <p>A 57-year-old female patient presented with an abnormal shadow on a chest radiograph. Contrast-enhanced computed tomography revealed a partially enhanced cystic mass in the left anterior mediastinum. Another cystic lesion was detected on the left side of the trachea in the upper mediastinum. The anterior mediastinal mass was suspected to be a cystic thymoma, and thus, a left thoracoscopic surgery was performed for its resection. The mass originated from a left pulmonary hilar region and was covered by an independent visceral pleura. The feeding artery originated from the left pulmonary artery with no connection to the bronchus. Histopathological results revealed that the mass consisted of alveolar cells, bronchial epithelium, cartilage, and a cystic structure with highly viscous contents, and it was finally diagnosed as extralobar sequestration.</p> Conclusions <p>Extralobar sequestration should be considered a differential diagnosis for atypical anterior mediastinal masses near the hilar region, especially in patients with other congenital malformations.</p>