Periodontal diseases are a major health problem affecting tooth-supporting tissues. Among them, aggressive periodontitis is characterized by rapid progression, family aggregation, systemically healthy patients ( 1 ), and is subdivided into localized and generalized according to the extent of the disease. Microbiota plays a major role in the etiopathogenesis of these diseases, including Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia and Fusobacterium nucleatum. The aim of this work was to study the prevalence of these microorganisms in 50 Uruguayan patients with aggressive periodontitis. Detection was conducted with conventional bacteriological techniques and PCR. In the generalized disorders, a higher prevalence of F. nucleatum and P. intermedia was observed, although P. gingivalis and T. forsythia were also important. In the localized disorders, P. intermedia, F. nucleatum and A. actinomycetemcomitans were the main ones. A similar flora to other geographical locations was present in our country.