Mutans Streptococci, in particular S. mutans and S. sobrinus, are generally considered to be the prime etiological bacteria of human dental caries. The aim of this study was to determine the frequency of mutans streptococci in dental plaque in three groups of caries-free and caries-affected Venezuelan children aged 2-6, 7-12, 13-19 years, and their possible association with dental caries. The frequency of mutans streptococci was determined in samples of pooled dental plaque collected from all detectable sources of 30 (62.5%) caries-affected and 18 (37.5%) caries-free children. The samples were collected from all available tooth sites using a Hollenbak probe and immediately suspended in Ringer's solution, serially diluted and cultured in Mitis Salivarius (MS) agar for total streptococci determination and Mitis Salivarius Bacitracin (MSB) for isolation of mutans streptococci. The bacterial identification procedure was done using the API Rapid Strep System. The criteria used to determine dmft and DMFT was established by Klein and Palmer (1941). Mean dmft and DMFT were 6.4 +/- 3.2 and 4.4 +/- 2.9, respectively. Ten (33%) out of 30 caries-affected children harbored mutans streptococci. The species most frequently found were S. mutans (20%), S. sobrinus (10%) and S. rattus (3.3%). Meanwhile, in the caries-free group only 6 out of 18 children (33%) harbored mutans streptococci, specifically S. mutans and S. sobrinus, both at 17%, with no significant difference between the two groups. These results indicate that the percentage of children that harbored mutans streptococci was similar in both groups, suggesting that other acidogenic species may be responsible for caries development.