Various types of non-tuberculous mycobacteria can be the aetiologic factors of chronic lung infections especially in patients with underlying chronic lung diseases. The aim of this study is to present the cases of pulmonary mycobacterioses observed in Institute of Tuberculosis and Lung Diseases in the years 1995-2001. There were 23 patients, 12 men and 11 women in the age between 35-77 years, mean 56 years. 16 out of 23 patients had underlying respiratory problems, mainly healed tuberculosis (7) and COPD (6). Two additional patients suffered from other diseases with potential immunosuppression (leukopenia). In 5 patients no disease other than mycobacteriosis was found, but they were chronic smokers. In 19 cases cough and expectoration of purulent sputum lasting from several months to several years was observed. In 5 patients onset of disease was acute or subacute with high fever. Eight patients had haemoptysis. In chest X-ray pathological lesions including (18 cases) lung cirrhosis (10) and cavities (15) were found. In 4 cases disseminated bronchiectases with small nodules were the main radiologic feature. Mycobacteriosis was caused by M. kansasii in 11 cases, by M. intracellularae in 6, by M. xenopi in 5 and by M. scrofulaceum in 1 case.