Does your case require an expert witness? If you need to prove an element of your case that requires specialized knowledge, you may need an expert witness. A classic example is a doctor. Under the rules of evidence, you cannot simply testify that you have a disease, like cancer. You only actually "know" you have cancer because a doctor has told you. You would need to have a doctor testify as an expert witness to accomplish that. The doctor, of course, is entitled to charge for his or her time. Between reviewing files, depositions and trial time, expert witness fees can add substantial cost to your case, but such testimony may be essential depending on your situation. Want to learn more about expert witness fees? The Expert Institute has a blog post about average fees by state and most commonly used fields here.