Aspergillus fumigatus, an important human pathogen, has been the subject of numerous epidemiological studies. This review gives a summary of the techniques used for revealing the genetic variability of A. fumigatus, including multilocus enzyme electrophoresis and methods based on DNA hybridization and amplification. Such studies have provided raw data for examining the structure of A. fumigatus populations. Several methods have been described for distinguishing recombination from clonality in fungal populations. In our studies, both the index of association test and the parsimony tree length permutation test were used for examining the reproductive mode of Aspergillus fumigatus populations. The tests were performed on isoenzyme and sequence specific DNA primer analysis data gathered from the literature. Both tests, together with other observations, supported the premise that recombination played an important role in A. fumigatus populations. A so-called epidemic population structure was observed in local populations isolated from patients. The prevalence of a single or some related electrophoretic types in such environments was attributed to some kind of selection pressure. Network methods were also used successfully to visualize the recombining structures of A. fumigatus populations. The applied techniques did not enable us to distinguish between the alternative hypotheses of whether past meiotic exchanges, parasexuality or a cryptic sexual stage were responsible for the recombining population structure of A. fumigatus.