The clinical and radiographic findings associated with the presence of hemivertebra ("wedge-shaped"vertebra) in small and brachycephalic breeds of dogs are reported together with the results of post mortem examination in the availabel cases. The condition is characterised clinically by progressive hind-leg weakness, spinal pain, abnormalities of the nervous system and evidence of muscle atrophy or other abnormalities of conformation. Confirmation of the clinical diagnosis is by radiography. It is suggested that the condition is congenital in origin. Breed incidences are reported. The occurrence of the disorder in certain families of dogs suggests also that it may be hereditary. Other congenital abnormalities are seen in some dogs affected by hemivertebrae.