Community oral health care projects in Thailand were tested for their effectiveness, especially in prevention of dental caries. Epidemiological baseline data on oral health status and attitudes of subjects age 5-44 years from six rural communities in northern Thailand were assessed. Caries experience in the permanent dentition was low but high in primary teeth. Periodontal status (CPITN) indicated poor oral hygiene and heavy calculus deposits. The majority of subjects perceived dental caries as the main problem. In prevention of occlusal caries, methods of pits and fissure sealants were evaluated in children aged 7-8 and 12-13 years in Bangkok. Delton sealants exhibited 93 per cent occlusal caries reduction and 83 per cent retention rate after two year application. Glass ionomer cement (GIC) sealants demonstrated significant caries reduction: 52 per cent (applied by dentist) and 74 per cent (applied by teachers), in the younger age group. A caries reduction (33%) of HF applications was a observed in the younger age group. Mutans streptococci were significantly related to caries prevalence and increments in both age groups. In treatment of carious lesions, the "Atraumatic Restorative Treatment" (ART) technique was evaluated in rural communities under field condition. It is based on minimal intervention, using hand instruments and not requiring electricity. After one year, the success rate of ART fillings for single surface fillings was 93 per cent in the permanent dentition and 79 per cent in the primary dentition.