SummaryThis paper describes a model for estimating the required capacity of alcohol treatment systems at the local or regional level. Previous attempts at developing comprehensive forecasting models for addiction services are briefly described. The four steps followed in the development of the present model are then outlined. In many respects, the resulting model is specific to Ontario, Canada. However, the general approach, and many of the underlying concepts and assumptions, may have wider application in assessing the need for alcohol treatment services.