Purpose: The aim of this study was to determine the prevalence of noncavitated occlusal dentine caries in permanent molars among students in a city with a low prevalence of caries. Combined radiographic and visual examinations were employed. Methods: The sample comprehended 1290 occlusal surfaces of permanent molars, in 179 students aged 12-15. The methods used were: visual inspection (VI), visual inspection with previous drying (VID) and Radiographic Examination (RE). For the statistic analysis, the DMFT and the DMFT modified (including RE, early lesions and microcaviteted lesions) indexes were used. Results: The mean DMFT was 2.3 (sd=2.5), and 32.5% of the students were free from caries on the VI. Of the 918 surfaces scored as clinically sound on VI, 241 demonstrated radiolucency in dentine on RE and the noncavitated occlusal dentine caries prevalence (per individual) was 56.4%. Of the 404 surfaces scored as clinically sound on VID, 75 (18.6%) demonstrated dentine radiolucency and the noncavitated occlusal dentine caries prevalence was 35.5%. Including dentine lesions on RE, the mean DMFT was 3.1 (sd=2.3), and 13.4% of the students were free from caries. Conclusions: The radiographic examination is effective in epidemiological surveys. However, new methods to replace this method should be evaluated, because the difficulty of transportation hinders its frequent use.