Dissecting aneurysm of the vertebral arteries following chiropractic manipulation of the spine. A thirty-five years old man had a Wallenberg Syndrome following chiropractic manipulation of the spine. Plain films and hypocycloidal tomography showed a foramen arcuale on both side. Arteriography lead to the diagnosis of dissecting aneurysm of the vertebral arteries. The favourable course point to the value of the posterior communicating arteries and the spinal artery as collateral pathways of the vertebro-basilar circulation.