Introduction: Dental caries is a multifactorial disease with many contributing factors in the genesis of risk (11). Streptococcus mutans (SM) is a gram positive, facultative anaerobe commonly found in the human oral cavity. Described for the first time in 1924 by Clarke, is the main germ responsible for the caries disease (5, 9). In fact, SM produces an insoluble extracellular polysaccharide sucrose which plays an important role as a mediator of the adhesiveness, both as a cementing molecule for other microorganisms, and to create a protected site where the microorganism can proliferate (6, 9, 10). Its presence in the plaque is not equal for all people and is closely related to sugar consumption (9). Its transmission can take place early in the life of the child through the mother’s saliva (2, 3, 4, 8).The early acquisition of this organism is associated with Early Childhood Caries (ECC) and then creates a primary colonization which is hardly removed (1, 7). Paying special attention to the health of women and children, this work aimed to decrease the incidence of childhood tooth decay, streamlining preventive efforts in a population at risk. Methods: Since 1999, all women referred to our clinic in the second trimester of pregnancy or during childbirth were offered the opportunity to perform a simple test to measure the presence of SM in saliva and have been given some advice (diet, hygiene, fuoro-prophylaxis, dental visit). The sampling of saliva was performed after chewing one paraffin tablet for about 1 minute. For the microbiological examination the technique of dip-slide test (CTR bacteria, Ivoclar Vivadent) was used; results were classified according to semi-quantitative classes of microorganism concentration.Women were classified positive when bacterial concentration was 100000 CFU/ml. Besides a general advice on hygiene and diet, these women were invited to undergo a prophylactic treatment with chlorhexidine, a disinfectant with bactericidal properties against SM. Results: 84% of surveyed women adhered to the screening (29% pregnant women, 55% in the puerperium). In the 12-year study, 2170/7213 (30%) women had a positive saliva test and were administered chlorhexidine. Conclusions: By means of a prenatal screening involving different professionals (microbiologist, obstetriciangynecologist, pediatrician, oral-hygienist) we could assess the likelihood of vertical transmission of SM from mother to child, and give the mothers medical advice on the risk of tooth decay in children. Preliminary data on the incidence of caries in children of those women who tested positive at the screening, confirm that our program has an important role in preventing childhood tooth decay.