An inflammatory myofibroblastic tumor (IMT) is a rare disease and can occur in nearly every site of the body. The usual intrathoracic sites where an IMT has been recorded are the lung and bronchus. An IMT originating from the mediastinum has been rarely reported. A patient with a posterior mediastinal mass that was noticed incidentally on a chest X ray underwent mass extirpation. The pathologic diagnosis was an inflammatory myofibroblastic tumor. The tumor was positive for tuberculosis as determined by PCR. Tuberculosis can be thought to be the causative factor of the IMT in this case.