Atlantoaxial instability is a congenital neurologic condition predominantly affecting toy breed dogs. Neurologic signs of a cranial cervical myelopathy typically present at a young age and can range from cervical pain (hyperesthesia) to paralysis. Diagnosis is often based on survey radiographs, although advanced diagnostic imaging can facilitate surgical planning, allow evaluation of spinal cord parenchyma, and rule out concurrent neurologic conditions. Treatment options consist of medical or surgical management, with surgical management being preferable in patients with neurologic deficits or those with unresolved cervical pain despite medical management. The prognosis for surgery is generally favorable.