Studies indicate that previous caries experience can influence future caries development; however, caries-free individuals also may develop caries. The aim of this study was to examine the relationship between baseline caries experience and salivary mutans streptococci (SMS) levels as an indicator for predicting caries incidence in pre-school children. One hundred forty-eight preschool children (mean baseline age, 3-8 years) of low socioeconomic status were examined for dental caries and SMS levels at baseline and annually for 2 years. All children were identified at baseline as either caries free or caries positive. The 2-year delta dmfs scores for both groups were evaluated as 0, 1-2, 3-4, or > 4. The children's baseline SMS levels were categorized as low (0 CFU), moderate (1-50 CFU), or high (> 50 CFU), and were recoded to assigned ranges of 1, 2, and 3, respectively, in each year for longitudinal analysis. Both the caries-free and caries-positive groups had high SMS levels associated with the greatest delta dmfs, and when SMS ranges were added for the three examination years (minimum = 3, maximum = 9), the mean second-year dmfs scores varied directly as the sum of the ranges. Results from this study suggest that SMS levels may be useful in identifying and predicting future caries in preschool children, independent of baseline caries experience.