Much has been written in the general field of tort law about the cause-in-fact defense as contrasted with the legal concept of proximate cause, but the cause-in-fact defense is underemployed in medical malpractice cases tried in New York courts. The distinction between cause-in-fact, also referred to as "actual cause", and proximate cause is frequently important enough to present this defense opportunity for the malpractice defendant where situationally appropriate. In most cases, the plaintiff retains the burden of proving through expert testimony that the defendant has departed from the accepted standard of care, and separately that the departure or departures were a proximate cause of the injury complained of, warranting an award of damages to the plaintiff. Reliance upon expert testimony to establish a prima facie case of causal connection is a necessary element of any malpractice claim.