Background: No recent informations exists on periodontitis-associated subgingival microflora of the Romanian population. The occurrence, the interspecies relationships and the relationship with the basic clinical parameters for a group of five periodontal bacteria were determined in a Romanian study population. Methods: Subgingival microbial pool samples were obtained from patients with localized (LagP = 16), generalized (GagP = 24) and chronic periodontitis (CP = 14). A polymerase chain reaction technique was used to detect Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythensis (formerly Bacillus forsythus), Treponema denticola and Prevotella intermedia. The chi-square and Kruskall-Wallis non-parametric tests were used to assess the differences between the 3 diagnostic groups. Results: In all germs, excepted Aa, the detection frequency did not significantly differ between the CP, LAgP and GAgP groups. The detection frequency of Aa significantly differs, continuously increasing between the CP, LAgP and GAgP groups (p=0.016). The mean proportions of Aa was higher in GAgP than in LAgP and CP respectively (p=0.005). The mean proportion of Td was higher in LAgP than in CP and GAgP respectively (p=0.028). Conclusions: Results demonstrate that the five periodontal pathogens analyzed are strongly associated with Romanian periodontitis. In particular, Aa are more significantly associated with generalized aggressive periodontitis, while Td are more significantly associated with localized aggressive periodontitis. Keywords: periodontal pathogen microflora, Romanian population