Natural cloning and expression systems of mobile gene cassettes of class 1 and class 2 integrons play an important role in the mobilization and dissemination of antibiotic resistance genetic determinants in gram-negative bacterial human pathogens, especially in the hospital environment. Gene cassettes located in integron variable region determine the resistance to antibacterials (AB) of different functional classes. The purpose of the work is the detection and characterization of class 1 and class 2 integrons in gram-negative bacteria isolated in Moscow hospitals and other regions of the Russian Federation in 2003—2015. Clinical strains of gram-negative bacteria (n=1248) had predominantly the phenotype of multiple drug resistance (94% strains). Ten percent of strains were resistant to three AB functional groups, 19% — to four groups, 42% — to five groups, 17% — to six groups, 7% — to seven groups. A high level of resistance to beta-lactams is associated with beta-lactamase genes of blaTEM- (35% strains), blaSHV- (25% strains), blaCTX-M- (38% strains), blaOXA- (31% strains), blaVIM- (3% strains) u blaNDM-types (2% strains). Resistance to other ABs is associated with class 1 (59%) and class 2 (8%) integrons. Most of class 1 integrons (54%) and class 2 integrons (88%) contain integron insertions in their variable regions: 22 variants of gene cassette arrays in class 1 integrons and 4 variants in class 2 integrons. Gene cassettes of 31 types were identified during the study including the most common aadB, aacA4, aacC1, aadA1, aadA2, aadA5, blaVIM-2, dfrA1, dfrA7, dfrA12, orfC, orfE, orfY and sat1 cassettes associated with the resistance to aminoglycosides, chloramphenicol, sulfonamides and beta-lactams, as well as orf cassettes encoding proteins with unknown functions. Novel gene cassette arrays have been identified: dfrA12s-orfF-aadA2 (In1249) and dfrA1-IS911-sat1-aadA1 (not numbered).