Objectives To test the hypothesis that parental factors in early childhood influence approximal caries experience in young adults. Methods A cohort of 494 individuals was followed longitudinally from 1 to 20 years of age. Data were retrieved from parental interviews and questionnaires when the child was 1 and 3 years of age. At age 20, the participants underwent bitewing radiographic examination. Based on the number of approximal caries lesions (Da), stratified into initial (D-i) or manifest caries (D-m) and approximal fillings (Fa), the participants were divided into two main groups: those with: (a) 0 D(im)Fa (n = 244) and (b) amp;gt;0 D(im)Fa (n = 250). A subgroup was also created (amp;gt;= 8 D(im)Fa; n = 33). Results Toothbrushing with fluoride toothpaste at 3 years of age less than twice a day (OR 1.6, 95% CI 1.0-2.6) and the participants mothers self-estimation of their oral health care as "less than optimal" were important risk factors for developing caries (amp;gt;0 D(im)Fa OR 2.0, 95% CI 1.3-3.1). An interaction effect between toothbrushing at 3 years of age less than twice a day and consumption of caries risk products amp;gt; 3 times a day further increased the caries experience in young adults (amp;gt;= 8 D(im)Fa OR 8.3, 95% CI 1.8-37.8) together with maternal anxiety about dental treatment (OR 7.4 95% CI 1.6-34.6). Conclusions Parental factors in early childhood are associated with caries experience at 20 years of age.