Purpose: The first large-scale epidemiological survey on dental caries in Slovenia was conducted in 1987 and repeated in 1993, 1998, 2003, 2008, 2013 and 2017, using the same methodology. The aim of the study was to examine the trend of caries in 12-year-olds in Slovenia during a 30-year time period. The changes over time in caries experience were compared with disease trends observed in other European countries. Study Populations and Methods: The WHO National Oral Health Pathfinder Survey was applied in all seven surveys (1987–2017). The surveys were carried out in all nine geographical regions of Slovenia. For each subject, the caries experience and presence of sealants were recorded. Results: The mean DMFT of 12-year-olds decreased significantly from 5.1 in 1987 to 1.5 in 2017 (p < 0.0001). The percentage of persons with sealed teeth increased from 6% in 1987 to 94% in 2017, and the percentage of caries-free persons increased from 6% to 42%. Conclusion: The implementation of a nation-wide preventive programme was determined to significantly contribute to the effective control of caries and continuously improve the oral health of Slovenian children. In an international perspective, the Slovenian achievements in disease prevention in terms of caries prevalence reduction may be important for other countries of the region.