You need an expert witness in a car accident if you are in a court and jurisdiction that requires a medical expert to connect the victim's injuries and the motor vehicle crash at issue. You do not need an expert witness if you are suing for less than $30,000 in Maryland. There is a mechanism to introduce the medical records and bills without an expert. If you are suing for more than $30,000 you need a medical expert to testify that the injuries were caused by the accident. The medical expert - make it a medical doctor to be safe - must testify that thee medical bills for which you seek reimbursement were fair, reasonable, and causally related to the crash.