The vitality of a region is frequently assessed by looking at its population growth pattern. This is seen as being linked to its economic and social vibrancy. To better understand the dynamics of this growth pattern it is necessary to decompose population growth into the contributions of natural increase (births less deaths) and migration (both domestic and international). This provides a demographic accounting of the factors of population change which we use to analyse the degree to which the levels and impacts of these factors differ between the Regional Council Areas of New Zealand. We find large variations between Regional Council Areas in overall population growth for the three quinquennia between 1986 and 2001. The Auckland region experienced the largest growth, coming both from high natural increase and international migration, while the “sunbelt” regions of Bay of Plenty, Nelson-Tasman and Marlborough had high growth, but driven by internal migration. In other regions, such as Gisborne, West Coast and Southland population growth declined.