Mycobacterium avium is an important veterinary pathogen causing avian tuberculosis in birds. The aim of the study was to evaluate the genetic relatedness in M. avium isolates from deep tissues of farmed lesser white-fronted geese with avian tuberculosis and in samples from the farm environment. The strains were analyzed by two PCR-based typing methods, inverted repeat (IR) typing and random amplified polymorphic DNA (RAPD) analysis. The primers for the inverted repeats of the insertion sequences IS1245 and IS1311 were used in IR typing, and the RAPD analysis was performed with six primers. Seven of the nine avian strains yielded an identical pattern in the IR typing, but they could be divided into two groups in the RAPD analysis. The remaining two bird isolates had an identical IR pattern (IR cluster II) which they shared with two environmental isolates. However, the RAPD analysis revealed that these environmental isolates had a RAPD pattern (RAPD cluster VI) distinct and different from either of the bird isolates (RAPD clusters II and IV). In all, four M. avium strains were verified as being inducers of avian tuberculosis in birds, and all were distinct from the three environmental strains identified. Thus, the results did not confirm the preliminary idea that a single strain had caused the epidemic. The polymorphism among M. avium strains highlighted the great biodiversity among an M. avium population even in a limited environmental setting during a short time span, and indicated the high susceptibility to avian tuberculosis of lesser white-fronted geese.