The aim of this cross-sectional study was to assess differences in caries experience according to socio-economic status (SES) in a health-care system with full coverage of dental costs for children up to the age of 18 yr. In 2011 and 2014, by performing hurdle negative binomial models, we obtained data on 3,022 children and young adults aged 5, 8, 11, 14, 17, 20, and 23 yr, living in four cities in the Netherlands. At all ages between 5 and 23 yr, the percentages of children with caries-free dentitions were lower and mean caries experience were higher in low-SES than in high-SES participants. In 5-yr-old children with dmft > 0, mean caries experience was 3.6 in those with low SES and 2.3 in those with high SES. In 23-yr-old participants, these estimates were 6.8 and 4.4, respectively (P < 0.05). Low-SES children have a greater risk of more caries experience than high-SES children. Thus, in a system with full free paediatric dental coverage, socio-economic inequality in caries experience still exists. Dental health professionals, well-child care doctors and nurses, general practitioners, and elementary school teachers should collaborate to promote oral health at the community level, with specific targeting of low-SES families. We further need policy measures to curtail, at community level, the increasing availability and consumption of highly processed, carbohydrate-rich foods, with particular attention for low-SES families.