Methods: a retrospective cohort study was undertaken, using data from the Data Retrieval in General Practice (DRGP) project in Northern Ireland, to identify a cohort of individuals aged 65 and over and living in the community at the outset of the study. A total of 28,064 individuals were followed up for 5 years to identify those who subsequently entered a nursing or residential care home. Controlling for the demographic, household composition and health characteristics of individuals, Poisson regression was used to estimate the incidence rate ratios of care home admission for 10 trusts. Results: a total of 24,691 of the initial cohort had complete information for all variables and were included in the final analysis; 1,313 (5.3%) had entered a care home at the end of the 5 years of follow-up. Admission increased significantly with age, and diagnoses of dementia and stroke. Controlling for the age, sex and health composition of individuals, some variations in admission rates were found across trusts. Conclusions: the study has highlighted the importance of age and clinical conditions as risk factors for care home admission. In addition, it appears that the area of residence might be important in determining a person's risk of care home admission. Such differences may be attributable to particular characteristics of the trust, such as the level of deprivation or degree of rurality, or to differing policies in relation to services for older people. More work is required to identify the causes of the differences to allow policies to be implemented to ensure equitable access to care homes across Northern Ireland.