Abstract The dermatologist's concern about adverse reactions to drugs can be viewed from two perspectives. Most often, dermatologists are confronted with skin reactions to drugs used in the treatment of a wide variety of noncutaneous diseases. Less frequently, but sometimes more dramatically, dermatologists care for a patient who may have developed a noncutaneous adverse reaction that can be attributed to a drug used in the treatment of a skin disease. Although skin reactions are among the most common undesired effects of drug therapy, there are relatively few systematic sources of information about the incidence, severity, and ultimate health effects of adverse cutaneous reactions associated with drug use. To understand the magnitude of the problem of cutaneous drug eruptions, one must first critically examine the sources of data about these events. In the first section of this chapter, criteria for evaluating the likelihood that a given drug is responsible for a given adverse reaction are briefly reviewed. The second section reviews methods used by drug surveillance systems in attempts to identify the incidence and severity of cutaneous reactions to drugs, as well as the incidence and severity of noncutaneous reactions to drugs used in dermatologic therapy. The third section reviews illustrative results of surveillance systems—including the American Academy of Dermatology's Adverse Drug Reaction Reporting System—which have provided information on the incidence of cutaneous drug reactions, causes of specific cutaneous drug eruptions of unusual severity, and adverse reactions to drugs used in dermatology.