This paper reviews issues of pharmacovigilance, defined as “all scientific and data gathering activities relating to the detection, assessment, and understanding of adverse events”, including pharmacoepidemiologic studies, which are “undertaken with the goal of “identifying adverse events and understanding, to the extent possible, their nature, frequency, and potential risk factors”. Some of these activities could be carried out more effectively. Particular attention is paid to the use of prospective observational studies and registries as important tools in this regard. Indeed, in studying drug safety, there are many situations in which the use of observational research has definite advantages over the randomized controlled clinical trial. While some controversy persists about the usefulness of observational research in the study of beneficial, intended effects, fewer objections have been raised about the usefulness of observational research in the study of drug safety, i.e., in assessing harmful, unintended, usually unanticipated outcomes.