Significant regional disparities in life expectancy were found in a previous study of Irish mortality. An attempt is made in the present paper to assess the relative importance of each of the major causes of death to an understanding of regional disparities in total mortality, using a specially devised index known as a partial standardised mortality ratio. It is found that regional disparities created by each of the major causes of death tend to have a reinforcing effect, although cerebrovascular diseases tend to conform less closely to the patterns established by the other major causes (viz. cardiovascular diseases, malignant neoplasms and respiratory diseases). Cardiovascular diseases exert the strongest influence upon the overall pattern, but malignant neoplasms exert a much stronger influence than might be expected given the number of deaths from cancer. Regional disparities are stronger for males than for females, suggesting lines for further causal investigation.