Adverse drug reactions (ADRs) are a common cause of dermatologic consultation, involving 2 to 3 per 100 medical inpatients in the United States. Female patients are 1.3 to 1.5 times more likely to develop ADRs, except in children less than 3 years of age, among whom boys are more often affected. Certain drugs are more frequent causes, including aminopenicillins, trimethoprim-sulfamethoxazole, and nonsteroidal antiinflammatory drugs. Chemotherapeutic agents commonly cause adverse reactions to the skin and nails, with certain agents causing particular patterns of reactions. ADRs can involve any area of the skin; the appendages, including hair and nails; as well as mucosa.