Lactobacilli appear in the oral cavity during the first years of a child's life. Their presence depends on numerous factors such as the presence of ecological niches e.g. natural anfractuosities of the teeth.A strong correlation has been established between the saliva Lactobacillus count and dental caries, the higher the DMF index, the higher the number of children harbouring a high Lactobacillus count.Among children, the presence of lactobacilli in coronal caries is incontestable. Among adults, lactobacilli are found in root caries. Since 1999, taxonomical revisions make it difficult to interpret the results obtained in the numerous previous studies carried out on the identification of oral lactobacilli, but whatever the sampling method or the identification technique, the carious site or the age of sampled subjects, most species belong to the Lactobacillus casei group.This is important because if a specific correlation can be found between few species of lactobacilli and caries a better understanding of their properties could allow the development of new tools for prevention.