Pneumothorax is an important and dangerous complication of pulmonary tuberculosis. Forty-six pneumothorax cases complicated with active pulmonary tuberculosis at National Chiba-Higashi Hospital were studied retrospectively. From Jan. 1987 to Dec. 1997, we experienced 3611 patients with pulmonary tuberculosis, and among them 46 patients (18-90 years old, 38 males and 8 females) had pneumothorax. On admission, 33 out of 46 cases (71.7%) were smear positive by sputum examination of mycobacteria and 41 out of 46 cases (89.1%) had cavitary lesions on chest X-ray. Eleven cases had mild pneumothorax, thirty-two had moderate, and three had severe. Pneumothorax was present on admission in 23 patients and developed during treatment for tuberculosis in the other 23 patients. Eleven patients were treated with bed rest alone, four were thoracentesis and aspiration, twenty-four were intrathoracic tube drainage and seven were operated. Thirty-one patients were recovered, but fifteen passed away, among them 13 due to respiratory failure. The Prognostic nutritional index (PNI; 10 x serum albumin concentration +0.005 x peripheral lymphocyte count) which was proposed by Onodera, serum albumin level and Body mass index were lower in the fatal group than in the survival group. We consider these indices are useful to evaluate the prognosis of active tuberculosis patients complicated with pneumothorax.