There is an urgent and growing need for population projections that are not only detailed by geographic unit, but are also detailed by demographic characteristics. A high level of disaggregation allows the planner considerable flexibility to aggregate the projected data in a variety of geographic and demographic configurations. This study reports on the methodology and results of the Massachusetts experience in developing detailed population projections. Combining conventional with some not-so-conventional techniques, population projections are developed for 351 geographic units, as well as 108 demographic categories. The projections are currently in use in a large variety of public and private planning activities. © 1989.