In order to evaluate suitable strategies for control of dental caries, a longitudinal study of caries progression has been initiated among 12-year-old children in Kaunas, Lithuania. The aim of the present paper was to describe the baseline caries situation in a sample of 12-year-olds, who had been examined using caries diagnostic criteria which differentiate between active and inactive caries lesions at both the cavitated and non-cavitated levels. The mean fluoride concentration in the drinking waters of Kaunas is 0.16 mg/l. A total of 889 children in the 6th grade from seven selected schools were examined. Each tooth surface of all permanent teeth was classified according to one of the following criteria: 0 = sound; 1 = active, surface intact; 2 = active, surface discontinuity; 3 = active, cavity; 4 = inactive, surface intact; 5 = inactive, surface discontinuity; 6 = inactive, cavity; 7 = filled; 8 = filled with inactive lesion; 9 = filled with active lesion; X = extracted. Distinction between active and inactive lesions was made on the basis of a combination of visual and tactile criteria. Virtually all children (99.7%) had experienced at least 1 DMF surface. The mean DMFS was 15.8. Half of the mean caries experience consisted of surfaces with active lesions (7.9), of which two thirds (4.9) were non-cavitated. The mean number of surfaces with non-cavitated inactive lesions was 4.4. The mean DMFT constituted 7.9; 95% of all first molars were affected, followed by the second molars (61%). A comparison of the caries profile according to the present caries diagnostic criteria with those recommended by WHO revealed that the WHO criteria yielded much lower DMFS and DMFT values, because this scoring system does not include non-cavitated caries lesions. The high level of non-cavitated active caries lesions suggests that in this population caries may to a large extent be controlled by simple preventive measures including use of topical fluorides.