We reviewed 72 patients with coexisting lung cancer and pulmonary mycobacteriosis, and discuss the features and transition of these coexistent cases. There were 56 pulmonary tuberculosis (PTB) cases and 16 non-tuberculous mycobacteriosis (PNTM) cases, 62 men and 10 women, with a mean age of 69 years. In 43 cases, both diseases were concurrently detected, lung cancer was first detected in 19 cases, and mycobacteriosis was first detected in 10 cases. The frequency of lung cancer in cases with active pulmonary mycobacteriosis was 1.2%. Pulmonary mycobacteriosis was characterized by Type II (40 cases) and Spread 2 (42 cases) on chest X-rays; the most frequent histologic type of lung cancer was squamous cell carcinoma (32 cases) and most were stage III-IV cases (57 cases). After PTB treatment, the negative conversion rate of sputum cultures in both the concurrently detected group and the group in which lung cancer was initially detected was 56% within one month and 94% within 2 months. For the treatment of lung cancer, 33 cases received supportive care, 13 patients underwent resection and 17 received chemotherapy or chemoradiotherapy. In PNTM cases, both lung cancer and pulmonary mycobacteriosis showed a slight state compared to those in PTB cases, and in the group in which lung cancer was initially detected, both diseases were more advanced or severe than those in the concurrently detected group or in the group in which mycobacteriosis was initially detected. The rate of coexisting lung cancer and pulmonary mycobacteriosis was unchanged at 1-2%, and the incidence of stage IV lung cancer cases has increased recently. Coexisting lung cancer and pulmonary mycobacteriosis is an important condition in respiratory disease in Japan. Physicians should be aware of the possibility of PTB coexisting with lung cancer.