Two patients with vertebral artery dissecting aneurysm are presented in which the posterior inferior cerebellar artery (PICA) arose from the wall of the aneurysm. The patients presented with progressive myelopathy due to mass effect on the medulla. One patient was treated with proximal occlusion of the vertebral artery using Guglielmi detachable coils (GDCs). The other patient underwent complete excision of the aneurysm, with reimplantation of the PICA into the vertebral artery proximal to the dissecting aneurysm. We obtained good results with improvement of myelopathy in both patients, but the patient who underwent bypass surgery suffered longstanding palsy of the lower cranial nerves. This report emphasizes that complete aneurysm clipping or excision for such patients is the gold standard of treatment, but preservation of PICA flow may require technically sophisticated surgical techniques. However, even if the aneurysm is not completely eliminated, the myelopathy can be dramatically improved with conservative endovascular treatment with proximal occlusion. Therefore, the choices for treatment in such lesions varies with the angiographic findings, degrees of mass effect on the brainstem, and the patient's physical condition.