What is the cause of sudden headaches for someone who has no history of headaches?

New onset headache: There could be many causes for new headache but a neurologist always assesses for the worrisome reasons, like an infection in sinus or teeth, early meningitis (infection in spinal fluid), west nile virus or most worrisome, some sort of tumor. If you have a new headache, best to see your doctor to consider referral to neurologist.