This paper analyzes sport and fitness malpractice suits in the United States and Canada, emphasizing the responsibility of doctors, along with some application to physiotherapists, trainers, or athletic therapists. The number of suits is felt to be limited but growing rapidly in both countries. The issues discussed include duty to patients (contractual duties and duties of independent contract), duty to third parties, the standard of skill and care, general and approved practice, expert evidence, "res ipsa loquitur," consent to treatment, and allied professions. Breach of contract, which can be a breach of the duty of care whether or not there is a contract, is discussed, followed by awarding of damages. A table presents 7 Canadian and 16 American cases which illustrate various principles of malpractice. The cases deal with such legal issues as the doctor as guarantor of care, failure in course of treatment, errors in judgment, providing reasonable medical assistance to athletes and failure to treat, application of workmen's compensation legislation to professional athletes, voluntary participants in sport assuming risks in the sport, negligence, battery, informed consent, and failure to communicate. (JDD)