The term "drug-induced neurologic disorders" refers to unintended or undesirable effects on the nervous system caused by drugs or associated with drug use. These may be drugs for neurologic or other diseases. In this clinical article, Dr. K K Jain, a neurology consultant in Basel, Switzerland, discusses the pathophysiology, epidemiology, diagnosis, and treatment of drug-induced neurologic disorders. The toxic effect on the nervous system may be primary or secondary to systemic effects of the drug. Pharmacogenetics, the study of influence of genetic factors on the action of drugs, is relevant to adverse drug reactions. Polymorphisms in the genes that code for drug-metabolizing enzymes, drug transporters, drug receptors, and ion channels can affect an individual's risk of having an adverse drug reaction. The approach to management is prevention and withdrawal of the drug responsible for the adverse reaction. Genotyping may identify patients who would develop adverse reactions to certain drugs; those drugs should be avoided in the identified subsets of patients.