1. The antero-posterior or sagittal diameter of the cervical spine has been measured radiographically in fifty-one Japanese men who fell into three groups-twenty with normal cervical spines, eleven with spondylosis but no neurological symptoms, and twenty with spondylosis and myelopathy.

2. The average normal diameter was found smaller by 2·25 millimetres in Japanese men than in European adults examined by other authors.

3. The average initial diameter in cases of spondylosis without neurological symptoms was found to be greater than normal, which suggests that the increased space round the cord helps to avoid compression.

4. The average initial diameter in cases of spondylosis with myelopathy was found to be less than normal, which suggests that compression may be determined by moderate osteophyte formation or disc protrusion.

5. The risk of myelopathy would appear to be high when the average diameter is 12 millimetres or less.

6. The difficulty with such radiological measurements is that standard lateral films cannot always record the degree of encroachment by disc protrusion or by hypertrophy of the soft tissues.