BACKGROUND: Measles has made a comeback in Western Europe, with more cases being reported each year. One factor behind this development is low vaccination coverage in socially disadvantaged segments of the population in many countries. This study investigates whether socioeconomic patterns of uptake of the measles, mumps and rubella (MMR) vaccine in the Nordic countries differ by national organisation of preventive health services for children. METHODS: MMR vaccine uptake before the age of two years was analysed in register data from Denmark, Finland, Iceland and Sweden, linked to family indicators of socio-economic status (SES) from national registers. RESULTS: Denmark, a country where child vaccinations are administered by general practitioners, presented the lowest overall coverage of MMR at 83%. It also had the greatest difference between subpopulations of low and high SES at 14 percentage points. Finland, Iceland and Sweden, countries where preschool children are vaccinated in 'well-baby' clinics, had a higher overall coverage at 91-94%, with a more equal distribution between SES groups at 1-4 percentage points. CONCLUSIONS: This study suggests that the organisation of preventive health care in special units, 'well-baby' clinics, facilitates vaccine uptake among children with low SES in a Nordic welfare context.