The size and distribution of Cortinarius rotundisporus genets at three sclerophyll forest field sites in New South Wales, Australia, were estimated by using microsatellite-primed PCR (MS-PCR) of DNA extracted from sporocarp tissue. MS-PCR fingerprints generated with the primers (GTG)5 and (GACA)4 indicated that two to five genets were present at each site, with each site being characterized by a single large genet (9–30 m in diameter). Analysis of internal transcribed spacer (ITS)-RFLP patterns from individual sporocarps used in the study suggested that three distinct RFLP types were present in the sampled C. rotundisporus population. ITS sequence data indicate that the three RFLP types had less than 88.4% sequence identity to each other, strongly suggesting that C. rotundisporus is a complex of three species.