The association between parents in Liverpool consenting to their children being invited for primary immunisations and five sociodemographic factors, namely sex, position of child in the family, family type, migration into Liverpool since birth, and local deprivation was examined. Rates of consent to invitation were over 97% for each antigen except pertussis, which had a consent rate of 83%. Consent to invitation for pertussis vaccine was least likely to have been given for boys, children with older siblings, those recorded as living with a single parent, and those in the most deprived areas. Local deprivation also had an effect on consent to the measles, mumps, and rubella vaccine. Migration into Liverpool had a significant effect on consent to invitation for all antigens except pertussis. The child's sex, family type, and local deprivation had no effect on consent to diphtheria, tetanus, and polio immunisations. Maximising pertussis vaccine uptake will require more attention to be paid to those parents who have been identified as being less likely to give consent. It is particularly important that consistent and clear advice about immunisations is made available to parents with two or more children, lone parents, and those living in materially deprived areas. Our findings challenge some of the assumptions underlying the principles of 'first parent visiting', at least so far as pertussis is concerned.