1. Fifteen patients with association of active pulmonary tuberculosis and primary pulmonary carcinoma are presented. The difficulties of differentiating the two diseases are discussed. 2. All data are analysed as to their value in arriving at an early diagnosis, of primary pulmonary carcinoma in patients with active pulmonary tuberculosis. 3. Some features which led to suspecting pulmonary carcinoma in the presence of active pulmonary tuberculosis such as atypical x-ray appearance, failure of clinical and radiological improvement on antibiotic treatment and the appearance of hilar shadows are described.