malpractice, Negligence, misconduct, lack of ordinary skill, or breach of duty in the performance of a professional service (e.g., in medicine) that results in injury or loss. The plaintiff must usually demonstrate a failure by the professional to perform according to the field’s accepted standards. Physicians, lawyers, accountants, and other professionals have increasingly been subject to malpractice suits in the U.S., causing a dramatic increase in malpractice insurance rates.