Intrathoracic kidney is a rare congenital anomaly, with only about 50 cases reported in the literature to date. It comprises less than 5% of all ectopic kidney disorders. However, it should be included in the differential diagnosis of posterior mediastinal masses as confirmation of the diagnosis obviates the need for further clinical studies, further treatment, or unnecessary surgical operation. Chest computed tomography is an important and efficient tool in confirming the diagnosis. We report a case of a 72-year-old woman who suffered from nonspecific chest pain for 3 years. Chest radiography revealed a left posterior mediastinal mass which was later confirmed by chest computed tomography to be a congenital intrathoracic kidney.