Abstract Introduction: The aim of the present study was to determine the prevalence and determinants of salivary Streptococcus mutans, Lactobacillus and Aggregatibacter actinomycetemcomitans and the associated risk of development of dental pathologies on a sample of Portuguese adolescents. Materials and methods: A cross-sectional study was designed including a inal sample of 447 adolescents aged between 12 and 18 years old, attending a public school in Sátão, Portugal. A self-administered questionnaire was illed out by the adolescents. Clinical examination of oral health status was carried out and saliva collection was accomplished by the passive drool method. The identiication of the different types of bacterial strains was accomplished using the Polymerase Chain Reaction technique. Results: The prevalence of S. mutans in the studied sample was 99.5% Lactobacillus, 80.8% S. mutans and 15.2% A. actinomycetemcomitans. The presence of S. mutans was associated with gender (male = 76.1% vs female = 83.6%; P = .04) and dental pain in the presence of severe dental caries (77.3% vs 87.8%; P = .006). The infection with A. actinomycetemcomitans was associated with age (