Thoracic splenosis is the autotransplantation of splenic tissue into the pleural cavity, usually following traumatic injury that simultaneously involves the spleen and diaphragm. Intrathoracic splenosis is an uncommonly reported phenomenon. We present a case of intrathoracic splenosis in a patient with a chronic aortic pseudoaneurysm, both detected, incidentally, three decades after the traumatic event. The diagnosis of thoracic splenosis can be confirmed noninvasively, using 99mTc sulfur colloid nuclear scintigraphy.