Population registers have formed the basis for computerised call/recall registers for screening programmes in many countries and have been important in achieving high uptakes in targeted populations. The absence of a population register for the ECCLES (European Campaign against Cancer, Localisation, Evaluation & Screening) Breast Screening Project necessitated the development of a special register of women in the target age group. The data sources used to build the project register were the Eastern Health Board and North Eastern Health Board General Medical Services database, Voluntary Health Insurance data and self-registration with the project. The register captured 86.3 per cent of the target population. A debate on the merits and difficulties associated with the setting up of a population register in Ireland is now timely.