Since I retired from the Army (1991) and started having to go to civilian doctors, I have been asked that question only once by a doctor. The question was on one of the forms I had to fill out and I left it blank. When I got in to see her, she was absolutely livid that I had not answered that question and, quite aggressively, informed me that I had to answer it as it was the law. When I was finally able to quit laughing, I grabbed my forms, further infuriating her, and left. Found another, far less confrontational and far less nosy, doctor. Bottom line is this: The doctor can ask any question they wish to. If that question is not directly connected to the reason you are seeing the doctor, nothing says you have to answer them.