Sixteen of 758 lung cancer in patients (2.1%) were found to have coexisting pulmonary tuberculosis. Of the above 16 of 758 patients (fifteen men and one woman), 4 of 214 patients (1.9%) were found from 1988 to 1989, and 12 of 544 patients (2.2%) from 1991 to 1994. In six patients, pulmonary tuberculosis and lung cancer were found at the same time by clinical work up. In five cases each, pulmonary tuberculosis preceded lung cancer, and lung cancer preceded pulmonary tuberculosis, respectively. Ten patients had adenocarcinoma, 4 had squamous cell carcinoma, and one each had large cell carcinoma and small cell carcinoma, respectively. Five patients were in stage "II", one in "IIIa", two in "IIIb", and eight in "IV" of clinical stage of lung cancer. As regards extent of pulmonary tuberculosis, one patient was in category "II" of the classification of the Japanese Society for Tuberculosis, 13 were in "III", and two were in "IV". Among 544 lung cancer patients from 1991 to 1994, 9 of 151 patients (6.0%) with a past history of pulmonary tuberculosis, had active pulmonary tuberculosis, and 3 of 393 patients (0.8%) with no history of pulmonary tuberculosis, had active pulmonary tuberculosis (statistically significant; p < 0.005). Five smear-positive patients were transferred to a tuberculosis hospital or a tuberculosis ward, and the remaining 11 patients were treated in isolation in the ward where they were. The efficacy of anti-tuberculous chemotherapy was almost comparable to that in patients without lung cancer. However, prognosis was poor, in line with that of lung cancer. Main discussion was devoted to the reason why the incidence (in association with tuberculosis) of adenocarcinoma exceeded that of squamous cell carcinoma in our present study at variance with the studies of other investigators.