Tan spot of wheat caused by Pyrenophora tritici-repentis is one of the most important diseases of wheat in Brazil. Under favorable environmental conditions, wheat yield can be reduced drastically. In the recent years in Brazil, tan spot caused severe yield loss due to the lack of resistance in the available Brazilian cultivars. There are at least eight races of the pathogen which produce different combinations of host selective toxins (HSTs) that are involved in pathogenesis. In Brazil there has been no report of the occurrence of different races of the pathogen. The objective of this study was to identify the prevalence of the different P. tritici-repentis races present in the Brazilian population. Pathogen isolates were collected from wheat growing regions of the south of Brazil during 2007 and 2008. The identification of the races is carrying out by inoculation onto a set of widely accepted differential wheat lines. Based on this methodology, the data showed that the population evaluated consisted of approximately equal amounts of race 1 and 2 indicating that these races are the most prevalent throughout Brazil.