Medical necessity cases continue to be a focal point for False Claims Act (FCA) investigations and lawsuits. With this focus comes an age-old problem for health care providers and entities defending these actions: the so-called “Battle of the Experts.” In these types of cases, the U.S. Department of Justice (DOJ) and/or a relator challenge a diagnosing doctor’s opinion that a procedure or service was medically necessary. As a result, the complaint alleges that the follow-on reimbursement claim submitted to the applicable federal health care program was “false” for the purposes of the FCA. A successful defense in these cases may ultimately hinge simply on whether the jury believes (or likes) the plaintiff’s or the defendant’s testifying expert more.