Purpose: To describe oral health status and to evaluate the effectiveness of a caries prevention programme in preschool children. Materials and Methods: A sample of 1656 3- to 7-year-old children were examined in kindergartens in 2002, and 411 3-year-old children were then selected to participate in the prevention programme. The test group A (n = 156), group B (n = 118), and the control group (n = 137) were defined for the study. For test group A, supervised toothbrushing was prescribed and for test group B, fluoride gel applications were used. For the control group, children did not undergo any of the aforementioned procedures. Dental caries was assessed according to the World Health Organization (WHO) criteria, and oral hygiene according to the Greene-Vermillion simplified oral hygiene index. Preventive programmes were based on oral hygiene instructions, supervised daily toothbrushing, and fluoride gel applications. The relationship between oral hygiene and severity of dental caries was determined by using Fisher's test. Results: The prevalence of dental caries varied between 39.7% and 90.8%, and the decayed, missing, and filled teeth (dmf-t) varied between 1.3 ± 0.16 and 5.0 ± 0.24. Oral hygiene was satisfactory in 43.2% of children. During the 3 years of the programme, a significant difference was found between the test and the control groups. The reduction in test group A was 45.4% and in test group B was 60.1%. Conclusions: The prevalence and severity of dental caries among the examined children increased with age, and was lower in both the test groups compared with the control group. The professional fluoride applications and proper oral hygiene showed the most effective results in caries prevention. Palabras clave: dental caries, kindergarten, oral hygiene, preschool children, preventive programme