In this paper we try to quantify the social cost of hospital waiting lists in Galicia, on the basis of the model by Cullis and Jones (1986). From official data of waiting lists for outpatient appointments published by the Galician Health Service (Sergas) and a survey of specialist doctors in the province of A Coruña, we estimate that the cost of waiting lists is 70 million euros annually. We argue that this estimate, which does not include surgical waiting lists, tends to be conservative. Finally, as a possible measure to reduce the costs of waiting, we propose the introduction of a copayment, which would bring about a direct efficiency gain from the reduction in waiting costs and an indirect “efficiency dividend” from the revenue of the copayment, which may reduce the need for market distorting taxes.