AIM: To investigate the prevalence of salivary mutans streptococci (MS) in children from a low socioeconomic multicultural suburban area and to evaluate if a 3-year comprehensive oral health education (OHE) program, initiated at the age of two years, had an impact on the saliva levels. STUDY DESIGN: Prospective clinical trial. METHODS: The material consisted of two cohorts of 6-year-old children from a suburban area in southern Sweden. One cohort (n=804) had participated in a OHE program with a focus on tooth brushing with fluoride toothpaste and flouride tablets added to the regular preventive care provided by the Public Dental Service. The second cohort (n=217) consisted of reference children only attending for regular dental care. Both cohorts were dominated by children with Arabic background. Salivary MS were evaluated by a chair-side test and caries was scored through clinical examinations. STATISTICS: Analyses were performed with Chi square tests, Pearson correlation coefficients and odds ratio calculations. RESULTS: The prevalence of salivary MS was high in both cohorts with approximately 90% harbouring the bacteria. One third of the children exhibited high counts (>10(6) CFU/ml) and there were no statistically significant differences between the groups. A statistically significant positive relationship between the levels of MS colonisation and caries prevalence was found in both cohorts. CONCLUSIONS: A 3-year OHE program implemented at the age of two years did not affect the high levels of salivary MS displayed in 6-year-olds living in a multicultural high-caries area.