Splenosis is defined as the autotransplantation of splenic tissue to abnormal locations after splenic injury. Although abdominal splenosis is the most common form and is usually discovered at laparotomy, thoracic splenosis is less common and occurs as an asymptomatic peripheral pulmonary nodule, incidentally discovered on a routine chest radiograph. Given the long interval between the initial trauma and its discovery, thoracic splenosis is rarely considered in the differential diagnosis of left-sided, pleural-based pulmonary nodules or masses. The diagnosis is often a result of surgery. The authors report an additional case of thoracic splenosis, review the literature, and discuss nonsurgical diagnostic methods.