The aim of this study was to investigate whether a relationship exists between ethnicity and uptake of the first dose of mumps, measles and rubella (MMR1) vaccination, and to study important factors influencing the parental decision about vaccination. Examination of routine data on uptake of MMR1 vaccine among children living in the London borough of Brent, North West London, for associations with ethnicity was carried out. Six focus group interviews were held and a questionnaire on factors related to immunisation by convenience samples of mothers from Asian, Afro-Caribbean and White backgrounds was completed. The routine data reported MMR1 vaccine status for 6444 children living in Brent who were aged between 18 months and 3 years on 1 December 2003. A total of 37 mothers took part in the 6 focus group sessions. Significantly higher coverage by MMR1 vaccine in the Asian population (87.1%) compared with AfroCaribbeans (74.7%) and the White group (57.5%) was noticed. The qualitative data revealed clear differences between the ethnic groups with respect to awareness of the controversy surrounding MMR vaccination (related to use of English-language media) and influence of grandparents and health professionals in decisions about immunisation. A multiple logistic regression model showed that although coverage of MMR vaccination increased with increasing socioeconomic status, there was no evidence of a statistically significant interaction between socioeconomic status and ethnicity. An important association between ethnicity and uptake of MMR1 vaccine is observed. This has implications for efforts to improve the currently inadequate levels of MMR vaccination across the population as a whole.