In health care systems such as Spain where patients do not pay the full price for health care services, waiting lists may be used as a rationing mechanism. The authors describe a theoretical model of the demand for and the supply of health care. They derive a waiting list function from the theoretical model that implies that waiting lists will increase as a result of increases in demand or reductions in supply. Then the authors estimate the obtained waiting list function. The results of the empirical estimation confirm the predictions of the theoretical model. Notably the recent recession has led to significant reductions in public expenditure of health care and caused longer waiting lists.