Future physician supply is a matter of concern in most industrialized countries due to its impact on cost and quality of health care. Consequently, forecasting the number of physicians becomes an important research issue from both methodological and policy perspectives. This article presents a simple forecast model developed for the State of Wisconsin (U.S.A.), using the complex federal model of the U.S. Graduate Medical Education National Advisory Committee as a backdrop. In this context, the article discusses the main determinants of physician supply, such as mobility, retention, ageing and productivity. The methodological issues in the simple modelling of such phenomena are examined using the Wisconsin case as an empirical example. Finally, policy implications of planning physician supply with respect to projected demand for services, changes in reimbursement patterns and productivity are discussed along with some of the recommendations actually made to the Wisconsin Legislature.