Almost one-third of newly referred hospital outpatients are suffering symptoms that cannot be explained by any recognised medical condition or disease.
The extent of this hidden epidemic has been revealed in preliminary results from the largest study of its kind.
It has implications for patients who hitherto have been largely ignored.
And could also be significant for the health service, which may be misdirecting resources because of incorrect diagnosis.
Scientists from Edinburgh, Glasgow, Dundee and Aberdeen university medical schools have found high levels of so-called functional somatic or medically unexplained symptoms in neurology referrals across Scotland.
Between 25 and 35 per cent of the 2,000 patients assessed at neurology centres were found to have no classical disease that could be responsible for their symptoms.
The scientists believe the problem is linked to how the brain interacts with other organs. They expect similar levels to be found in most medical specialities.
Peter Craig, research manager at the Scottish chief scientist's office, said: "What strikes you is the sheer volume of work in specialist clinics involving people who don't appear to have any distinct neurological symptoms and who are not going to benefit from specialist care in that setting."