Stenosis of the vertebral canal is a form of compressive stenosis in contrast to transport stenosis of vessels or other channels. The concept, definition and pathomorphological properties are discussed. As it is a form of compressive stenosis, the diagnosis is based on measurements of diameters rather than of cross-sectional surfaces. The biomechanical action of compressive stenosis is compression of the fixed living content at two opposite sites or at all sites. The special properties of sciatica in stenosis are described and presented in tabular form. Some properties of neurogenic intermittent claudication (I. Cl.) in the presence of stenosis are discussed. There is a predominance of sciatica at rest and of motor weakness during walking. The mechanism of neurogenic I. Cl. is obscure. Stenosis of the lumbar vertebral canal is one of the conditional determinants of I. Cl. The data presented in this paper demonstrate, however, that stenosis is not an absolute determinant of I. Cl. and that its production depends on the combination with other determinants. The theory is advanced that other determinants may be related to changes in the caudal nerve roots due to either constitutional properties or to subclinical changes induced by ageing and chronic wear and tear, and compression and traction in the area of stenosis during various bodily activities. Suppression of sciatica during I. Cl. is a phenomenon which is particularly difficult to explain.