Background: Idiopathic spinal arachnoid cysts are rare cystic masses of the spinal canal generally classified as intra- or extradural, based on anatomical presentation. However, this system may not effectively indicate treatment. Objective: To investigate the incidence, resection modality, and prognosis of spinal arachnoid cyst in a 15-year case series. Patients and methods: A retrospective study was conducted in 81 spinal arachnoid cyst patients (male: female 34: 47, mean age 36.5 years, age range 6-66 years) classified using a novel five-category T1-weighted and T2-weighted magnetic resonance imaging (MRI) classification system (intramedullary, subdural extramedullary, subdural/epidural, intraspinal epidural, or intraspinal/extraspinal). Conservative treatment failed in all patients. They underwent spinal surgery between January 1995 and December 2010 and were followed up for 69 (range 3-187) months. Performance outcomes were assessed using the Fugl-Meyer (FM) scale 90 days after operation. Recurrences and deaths were recorded. Results: Subdural/epidural and intraspinal epidural cysts accounted for 66.7% (54 of 81) of patients, but exhibited relatively lower rates of postsurgical improvement using FM, with only 66.7% (36 of 54) of patients showing improvements. Excellent outcomes using the FM scale were reached in 100% (eight of eight) of intramedullary, intraspinal/extraspinal, and subdural extramedullary cyst patients, 86.7% (13 of 15) of subdural extramedullary cyst patients, and 66.7% (36 of 54) of epidural intraspinal cyst patients. Conclusion: The proposed five-category multimodal MRI-based stratification system for spinal arachnoid cyst patients may more effectively allow clinicians to select the appropriate surgical intervention, and may help to predict outcomes.