Spinal arachnoid cysts are rare lesions that may produce symptoms by compressing the spinal cord or nerve roots. MRI is essential for diagnosing this entity. We retrospectively reviewed the medical charts, radiological examinations, and follow-up data of four adults with spinal arachnoid cysts diagnosed in our center over a two-year period (2007-2009). All cysts were located in the thoracic spine. Three were dorsolateral to the spinal cord and one was ventral. Most had multiple septa but one had a single septum. Cyst size varied greatly; one cyst extended through eight vertebral bodies. One patient treated expectantly died of cardiovascular problems one year after the cyst was diagnosed. The other three patients underwent laminectomy and cyst fenestration; two had clinical and imaging signs of relapse after surgery. One of the patients with a relapsed cyst worsened clinically, developing syringomyelia and requiring reintervention with shunting to the subarachnoid space. The outcome of the operation was good in the case of the single septum. Spinal arachnoid cyst is uncommon. Its diagnosis is complex because the symptoms are unspecific and the imaging findings are subtle. Spinal arachnoid cyst should be included in the differential diagnosis of chronic paraparesis. Imaging plays an essential role in the diagnosis, follow-up and management of spinal arachnoid cysts.