The medical expert witness invoice is issued by a health care consultant, usually hired for their testimony or deposition, who has been consulted for their knowledge in a particular medical field. This type of witness consulting is common in malpractice cases where a third (3rd) party expert can make a testimony and explain the standard medical procedures for certain illnesses and/or diseases. The medical witness will be called in to get their professional opinion on matters of negligence or non-standard procedures in regard to a physician charged for malpractice. A large percentage of expert witnesses will require a retainer up front and then will charge an hourly fee for file review/preparation and another higher hourly fee for their testimony. The invoice will include the date upon which all or a part of the payment will be due (depending on the arrangement made between the parties).