Aims. This study aimed to determine the actual proportion of children up to date with their immunisations and the improvement that could be made by surgery based recall measures, with a view to identifying (qualitatively) problems that affect comparisons with both the national survey and other practices. Methods. The immunisation status of 268 under 6 year olds from an urban Auckland general practice serving a poor, geographically mobile population was determined from clinic records, and other sources. A catch up programme was implemented where required and the proportion of children up to date with their immunisations measured again. Results. According to the practice records 50% of the children were up to date with their vaccinations at 1 September 1993. When the practice records were augmented by interviewing caregivers and other general practitioners the proportion of children up to date at 1 September 1993 was found to actually be 76%. This increased to 90% by 31 December with a surgery based recall system, and a further 7% had commenced but not yet completed a catch up programme. Conclusion. General practitioners can improve, relatively easily, recommended immunisation levels in poor and mobile populations, although vaccines due after 1 year of age may not be given on time. Problems limiting the validity of comparisons with other surgeries include the determination of the practice population, and of its demographics, as well as the process used to determine whether a child is up to date and the vigour with which that process is pursued. A continuous improvement model is suggested as an alternative to standardising, auditing, and weighting outputs from practices.