Of T 4 disease of lung cancer, malignant pleurisy and intrathoracic dissemination are the greatest factor preventing a cure, despite the best efforts of surgery and various adjuvant therapy modalities. Preoperative evaluation of this disease is of first importance using conventional radiology and computed tomography. Of the 43 patients who were intraoperatively diagnosed to be the disease, 8 (18%) appeared on the conventional radiology as small amounts of pleural effusion, and 9 (21%) with a interlobar pleural thickening. Based on CT findings, 16 (67%) had one or more of some disseminated nodules, interlobar pleural thickening and broad pleural indentation. In patients with T 4 disease, the 5-year survival rate was 14% in patients with malignant pleurisy and/or intrathoracic dissemination, compared with the 18% in those with direct invasion to great vessels, with no significant difference. According to intrapleural instillation as postoperative adjuvant therapy, the 5-year survival rate was 25% in the patients given interleukin-2, compared with 38 months of survival time for patients prescribed doxorubicin and 33 months for those underwent exploratory thoracotomy. A more favorable prognosis of patients whose malignant pleurisy and/or intrathoracic dissemination are first found at thoracotomy can be expected when postoperative intrapleural instillation of interleukin-2 is prescribed following the resection of the intrathoracic tumors.