Purpose: To compare prevalence and microbial load of six periodontal pathogens between Italian and Dutch patients affected by chronic periodontitis, using oligonucleotide probe technology. Materials and Methods: Subgingival plaque samples data from 352 Italians and 115 Dutch periodontal patients were analysed and compared. Bleeding on probing, suppuration, probing pocket depth, clinical attachment level, age, gender, ethnicities and smoking habits were recorded. Presence and level of bacterial species were determined by realtime polymerase chain reaction under the identical microbiological protocol. Statistical analysis was performed using the chi-square test, Mann-Whitney U-test and binary unconditional logistic regression (α = 0.05). Results: Between populations, only Treponema denticola and Porphyromonas gingivalis differed significantly, being more prevalent in the Italian group (p = 0.0001). Except for Tannerella forsythia, all bacterial loads differed significantly: Treponema denticola (p = 0.0001) and Prevotella intermedia (p = 0.001) were higher in Italians, while Porphyromonas gingivalis (p = 0.001), Fusobacterium nucleatum (p = 0.03) and Aggregatibacter actinomycetemcomitans (p = 0.001) were higher in Dutch patients. Conclusions: Significant differences in prevalence and bacterial load of periodontal pathogens exist between Italian and Dutch patients affected by chronic periodontitis. The microbiological profile, and particularly the bacterial load of pathogens, varied significantly between populations. Keywords: DNA microarrays, epidemiology, microbiology, periodontal disease, periodontitis