This paper challenges the conventional wisdom that, because of the free rider problem, a case can be made for compulsary vaccination against infectious disease. For a very general class of models, requiring that all individuals be vaccinated is strictly dominated by free choice. The market allocation is not optimum and in the full information optimum some individuals would be compelled to be vaccinated. This allocation can be achieved by taxes and subsidies; however, the government can exploit the revelation properties of vaccination and achieve an even better allocation than the full information optimum. © 1991.