My husband's 21 yo son was in a Motorcycle accident. His fault. He is under his dad's Insurance. We live in Missouri

His son is an adult, and bankruptcy can wipe out debt as long as no DUI

No, a parent has no obligation to pay for 21-year-old's medical expenses.

It isn't clear what unpaid medical expenses you are referring to - the son's medical expenses incurred in the accident or those of another person injured in the accident as a result of the son's negligent operation of the motorcycle. To the extent that you are asking if Dad is on the hook for an adult son's medical expenses the answer is no as already stated by the prior answers. If you are asking if Dad can be held liable for damages sustained by another person injured by the son's negligent operation of the motorcycle then the answer is probably not but possibly. Generally speaking, a parent is not going to be responsible for the conduct of a child. My 16 year old daughter drives now and if she were to cause a car accident I would not be legally liable for any damages she caused. UNLESS it could be shown that I negligently entrusted the vehicle to her. Since she is driving my old car which is still titled to me she cannot drive that vehicle without my permission. However, just because I give her permission to drive it and she causes a collision does not equate to my being liable as well. In order for me to have liability, I must have been negligent as well. That is where the idea of negligent entrustment comes into play. In order for me to have liability I have to know or have reason to know that my daughter is an extremely unsafe driver but nevertheless I entrust the car to her to drive. So if she had a bunch of prior accidents and/or a bunch of very serious traffic tickets such a careless and imprudent driving then it starts to look more like I know she shouldn't be driving so in letting her take the car now perhaps I have negligently entrusted the car and therefore could be liable. Hopefully that made some sense but also recognize that in order for me to held liable I have to have the legal right to deny access to the car to my daughter. Let's change the facts to be a different daughter that is at least 18 years old and has purchased her own car with only her name on the title. She still lives at home so the car is insured on our policy to get a better insurance rate. Even if I know that she is the world's worst driver and should never be permitted to operate a car on the open road I cannot be held liable for negligent entrustment as I have no legal right to keep her from driving the car since it is her car and not mine. Bottom line, if the question deals with being liable for medical expenses to someone injured by the son's negligent operation of the motorcycle it is highly unlikely that your husband will be responsible for any such expenses unless there is evidence that the son's was a truly terrible driver and knowing this Dad allowed him to operate Dad's vehicle. Hopefully that answers your question satisfactorily.