Four variables which are capable of measurements at the chairside were assessed for their ability to identify young children who would experience caries during the subsequent 1 1/2 yr period. The total of 92 children and their mothers participated the study. The age of the children at baseline was 19 months. The variables studied were: visible plaque on the labial surfaces of the maxillary incisors, the use of a nursing bottle, mother's caries prevalence and mother's salivary level of mutans streptococci. Visible plaque and the use of a nursing bottle were strongly associated with the caries development, while the other two variables had weak or no statistically significant associations. The best indicator of risk was visible plaque. Its sensitivity was 83%, specificity 92%, positive prognostic value 63% and negative prognostic value 97%. Overall, 91% of the children were correctly classified with this variable, while the corresponding percentage of the other variables ranged from 72 to 77. The results suggest that visible plaque on the labial surfaces of maxillary incisors of a young child is a sign of caries risk.