The aim of the study was to analyse complex structured data sets of ECC in 155 children. The children were 30 months old and 45% of their mothers believe that caries is a transmitted disease. For each child an index of caries (dmft) had been recorded together with the number of primary teeth, oral hygiene and gingivitis, salivary mutans streptococci (MS), and drinking behaviour at night with a bottle of soft drinks. Furthermore, a set of structured variables, such as mothers' characteristics (education, occupation) and their effort to control the toothbrushing of the child, was included. The cariogenicity of the food was registered as well. A conditional independence graph was used for analysis of data sets. Studying the graph, it was apparent that MS and dmft formed a separate set with the highest significance (phi 0,346). A negative correlation could be shown between mothers' education and serving of cariogenic food (phi -0,222) and MS counts (phi 0,214). Mothers with high education usually have an occupation (phi 0,21) and check up the toothbrushing of their children (phi -0,107), which have lower MS counts (phi -0,246). Children of mothers with an occupation were put to bed without a nursing bottle of soft drinks (phi -0,172) and had lower plaque indices (phi -0,161). Plaque correlated positive with caries decay, especially with rampant caries (phi 0,231). The results could show that children of mothers with low education have a high risk for ECC. In addition mothers need more information about early transmission of MS. Keywords: caries prevention, early childhood caries, knowledge of mothers, behaviour of mothers, mutans streptococci, transmission