Sixty-six dogs suffering from intervertebral disk diseases on cervical and/or thoracolumbar disks were treated by a ventral fenestration. The breeds affected with disk diseases were Dachshund (65.1%), Beagle (15.2%), Shih Tsu (4.5%), Pekingese (4.5%), and others (18.2%). Sites suffered from disk diseases and received disk fenestration most frequently were from T10-11 to L2-3. However, other disks were also needed the operation in some cases. An average number of disks received fenestration was 6.0. Days to walk after the fenestration in 51 cases varied 1 to 120 days (average: 14.9 +/- 22.0 days, mean +/- S.D.) depending on their severity. The recovery rates from the follow-up study were as follows: In grade I (3 cases, able to walk with back pain) and grade II (14 cases, slight ataxia and paresis) it was 100%, respectively. The rates in grade III (23 cases, paraplegia with positive deep pain) and grade IV (26 cases, paraplegia with lack of deep pain) were 73.9% and 65.4%, respectively. A few recurrence after the operation were observed in this study. As a result, the ventral fenestration was extremely effective as a treatment for disk diseases in the dog.