A cross-sectional study of 8204 children was performed to investigate the prevalence of immunization against measles, mumps and rubella and possible determinants of immunization uptake. The study was approached from a Lewinian perspective on preventive behaviour. Seventy-one questions referring to the guardian of the child, his or her partner, the household and the child, as well as to immunization-related experiences and situational topics were asked. Two psychological variables were studied: health locus of control and subjective relevance concerning measles. The immunization rate was 77.7 percent [95 percent confidence interval 76.8-78.6]. Multiple logistic regression yielded the following odds ratios for non- uptake of measles immunization: natural health orientation 8.74 [6.72-11.37]; advice of paediatrician 6.02 [4.67-7.75]; dangerousness of measles 2.00 [1.53-2.60]; marital status 1.87 [1.31-2.51]; assessed reliability of vaccination 1.57 [1.23-2.01]; smoking 1.55 [1.21-1.98]; and number of siblings 1.55 [1.21- 1.98]. Parents or guardians of immunized children were more internal and assessed measles as more relevant than those of non- immunized children.