Barré-Liéou syndrome, or posterior cervical sympathetic syndrome, has symptomatology related to underlying cervical instability. While classified as a rare disease, Barré-Liéou syndrome is likely underdiagnosed. Vertebral instability, occurring after neck ligament injury, affects the function of cervical sympathetic ganglia (located anterior to vertebral bodies). Symptomatology includes neck pain, migraines/headache, vertigo, tinnitus, dizziness, visual/auditory disturbances, and other symptoms of the head/neck region. Treatment for Barré-Liéou syndrome is suboptimal and often involves long-term use of pain medications, chiropractic care, or surgical fusion. Prolotherapy offers a noninvasive treatment option to ameliorate symptoms while treating the underlying cause of the disorder—cervical instability. In this case series, the results of eight patients from 2011 to 2013 who received prolotherapy for Barré-Liéou syndrome following longstanding symptoms after trauma are reported. All patients reported improvement of neck pain and associated symptoms and increased physical activity. Prolotherapy should be considered as treatment for Barré-Liéou syndrome.