The main causative agents of lung infection in patients with cystic fibrosis (CF) are P. aeruginosa, S. aureus and H. influenzae. In the last decade, gram-negative nonfermentative microorganisms (NFMO) - Вurkholderia cepacia complex (Bcc), Stenotrophomonas maltophilia, Achromobacter xylosoxidans and non-tuberculous mycobacteria, fungi of the genus Aspergillus have acquired the clinical significance. It is found that the chronic lung infection in 2/3 of the cases caused by association of microorganisms. Among hospitalized patients, in contrast to outpatients, these associations are represented by two, three or more species of microorganisms. The associations of P. aeruginosa + S. aureus (18,2 %) and P. aeruginosa + Bcc (9,1 %) are the most common. Other representatives - A. xylosoxidans, S. maltophilia and A. baumanii - is often identified in the associations of microorganisms. The focuses of chronic lung infections are formed in patients with increasing age. The dominant pathogens are P. aeruginosa and S. aureus. The methicillinresistant staphylococci and P. aeruginosa strains with a mucoid phenotype are of particular importance for cystic fibrosis patients. Bcc isolates from cystic fibrosis patients in Russia often belong to genomovar III A-B. cenocepacia. The Bcc strains colonize the lower airways of patients with CF and are able for long-term persistence and transmission from patient to patient. The resistance to many antibiotics is the main feature of the P. aeruginosa, S. aureus and Bcc strains. The strains of microorganisms with atypical phenotype (small colony variants) are formed under the action of the antibiotic. Infections caused by Bcc and other NFMO are difficult to identify and we need to use a wide range of bacteriological, biochemical, molecular biological techniques and mass spectrometry.