Syringomyelia (SM) is a debilitating neurological condition characterized by abnormal accumulation of fluid within the spinal cord. SM is most often observed with Chiari type I malformation (CM), an abnormality of the junction of the brain and spinal cord. When combined, CM and SM (CM+SM) cause serious problems, including chronic pain (headaches, neck pain, extremity pain); neurological deficits (weakness, sensory loss, loss of bladder control); and spinal deformity. Neurosurgical treatment can halt or even reverse disease progression, eliminating pain and preventing permanent neurological deficits or spinal deformity. Traditionally, this surgery involves posterior fossa decompression with duraplasty (PFDD), in which bone is removed from the base of the skull, and the covering of the brain and spine is surgically opened and expanded. However, this technique causes significant complications in 1 in 5 patients, prompting many patients and physicians to choose a less invasive posterior fossa decompression without opening the brain’s protective covering (PFD). Currently, there is no evidence indicating which approach maximizes symptom resolution and improvement in quality of life (QOL) while minimizing the risk of harm. To provide patients and physicians with this critical information, we propose a trial in which patients will be randomly treated with either PFDD or PFD, and we will compare: the harm to patients, change in symptoms, SM size, and improvement in QOL associated with PFDD versus PFD. These results will enable the creation of evidence-based treatment guidelines and, importantly, provide CM+SM patients and families with the information they need to make informed decisions about their health.