Through careful follow-up of a cohort, born March to August 1994, we have recorded the highest ever primary immunisation uptake figures for the Dublin area, with completed uptake for Diphtheria, Tetanus and Oral Polio of 92.1%, Haemophilus influenzae type b of 88.7%, Pertussis of 85.7% and Measles/Mumps/Rubella of 78.1%. Eastern Health Board uptake estimates for the same period are 8.1-21.4% lower. We believe the rigour of our data gathering explains this discrepancy. Evidence is reviewed in support of the hypothesis that Eastern Health Board databases underestimate true immunisation uptake.