The microbial population in 73 rapidly progressive periodontitis (RPP) lesions in 10 young adults aged 25 to 35 years (5 males, 5 females) was studied in relation to the clinical parameters probing depth, bleeding on probing, and suppuration, which were recorded at the sampled sites. Porphyromonas gingivalis was found to predominate (26.7%) in 73 periodontal lesions with clinical probing depth > 6 mm, followed by Bacteroides forsythus (23.6%), and Prevotella intermedia (15.7%). The prevalence of P. gingivalis was 91.7%, Fusobacterium nucleatum, 90.4%; Streptococcus intermedius, 87.7%; and B. forsythus, 53.4%. Significant differences between bleeding index 0, 1, and 2 (P < 0.05) in frequency of detection were found for P. intermedia, Campylobacter concisus, Selenomonas sputigena, and Peptostreptococcus micros at bleeding sites and for Streptococcus sanguis, Actinobacillus actinomycetemcomitans, and B. forsythus (P < 0.001) at non-bleeding sites. Between suppurating and non-suppurating sites, significant differences (P < 0.05) in frequency of isolation were found for P. intermedia, Capnocytophaga ochracea, and A. actinomycetemcomitans at suppurating sites and for F. nucleatum at non-suppurating sites.