Between 1799 and 1806, trials of vaccination to determine its safety and efficacy were undertaken in hospitals in London, Paris, Vienna, and Boston. These trials were among the first instances of formal hospital evaluations of a medical procedure and signal a growing acceptance of a relatively new approach to medical practice. These early evaluations of smallpox vaccination also relied on descriptive and quantitative accounts, as well as probabilistic analyses, and thus occupy a significant, yet hitherto unexamined, place in the history (...) of medical statistics. (shrink)