The original sample consisted of 179 randomly chosen children aged 6 years and 1 month at the time of examination. Of these children, those 88 were selected who had been exposed, since the age of 4, to consistent oral hygiene measures and dietary habits. The investigation involved clinical registration of caries, including subsurface lesions, and restorations in buccal and lingual surfaces in primary molars and cuspids. The mesial surface of second molars, distal and mesial surfaces of first molars, and the distal surface of cuspids were recorded from X-ray pictures. 85 children were classified as follows, beletary habits: (1) > 6 or (2) 5–6 meals and snacks a day including at least one ‘unsuitable’ Dack with a high-sucrose component, or (3) < 6 consumptions with suitable snacks sntween meals. Oral hygiene habits: (1) an adult brushed the child’s teeth at least once a day or (2) the children did it at least once a day themselves. The statistical analysis of the results revealed a clear tendency that the effectiveness in prevention of buccal and lingual caries by practicing one of the two habits at the most favourable level was greatest when the other habit was most unfavourable. This was not true for proximal caries, but, at both oral hygiene levels, the number of carious surfaces decreased with more favourable dietary habits. The validity of the results is discussed with proper consideration of the differences between neighbouring combinations.