Two major outbreaks of smallpox occurred in Brooklyn and New York around the turn of the twentieth century. Health officials moved aggressively to contain the disease, conducting mass vaccinations from house to house and in workplaces. Although these programs were ostensibly voluntary, the manner in which they were conducted was often coercive, giving many people the impression they had no choice but to submit. Officials portrayed their programs as voluntary because they lacked a clear legal basis for their actions and because they believed this was the most effective strategy for gaining public cooperation. This essay examines the events that surrounded a series of legal cases challenging the use of coercive measures to enforce vaccination during and after the smallpox epidemic of 1894, and the repercussions that this litigation had on disease-control efforts and popular attitudes toward vaccination and other measures. The cases described here were part of an extensive body of nineteenth-century jurisprudence on vaccination that was crucial for the evolution of public health police powers in general, and of vaccination policy in particular.