Cerebellar tonsillar descent is found in about 1% of health people. Whether or not this amounts to a Chiari malformation hangs in principle upon how far the tonsils descend; in practice however the key matter is obstruction of the foramen magnum, not the distance the tonsils descend. Normally, asymptomatic Chiari or tonsillar descent is best left alone; of MRI of the cervical cord shows a syrinx then surgery may be considered. Should such asymptomatic patients have follow up MRI? Probably not in mist cases.