The clinical, radiological and anatomical changes in a 6 1/2-month-old Fox Terrier bitch with congenital malformation and variation of the lumbar vertebrae are described. The dog has 5 lumbar vertebrae and the first lumbar vertebra was malformed resulting in a dorsal hemivertebra, kyphosis and spinal cord compression. The possible pathogenesis of the dorsal hemivertebra is mentioned.