BACKGROUND: Syringomyelia, secondary to adhesive arachnoiditis, is an intractable disease characterized by progressive extension cranially and caudally, resulting in severe neurological deficits. Subarachnoid-subarachnoid bypass has recently been reported for syringomyelia from trauma or spinal tumor surgery. METHODS: We investigated whether subarachnoid-subarachnoid bypass is a salvage treatment for refractory adhesive arachnoiditis of various etiologies, including arachnoid abnormality and hemorrhage. Patients who underwent subarachnoid-subarachnoid bypass between 2021 and 2025 for recurrent adhesive syringomyelia after conventional treatments were retrospectively reviewed. The primary outcome was the change in syrinx length from baseline to follow-up. Secondary outcomes included neurological outcomes and surgical complications. RESULTS: Six patients (median age 55 years; 2 men) were included. Patients had undergone a median of 2.5 conventional treatments, such as arachnoidolysis or intradural shunt placement, before subarachnoid-subarachnoid bypass. The syrinx showed temporary regression followed by re-expansion in all cases, attributed to extensive adhesions. Two patients presented with upper extremity paresis and pain, two with paraparesis, and two with severe paresthesia of the body trunk and lower extremities. After subarachnoid-subarachnoid bypass, the syrinx length showed a significant overall reduction (median, preoperative vs. postoperative: 9.5 vs. 5.0 levels; p = 0.014) in the median follow-up of 36 months. Neurological symptoms improved in five patients. Two patients were complicated with tube occlusion, which resolved with re-operation. CONCLUSIONS: Subarachnoid-subarachnoid bypass may be an effective option for refractory cases of syringomyelia not only from trauma or spinal tumor surgery but also from adhesive arachnoiditis due to arachnoid abnormality and hemorrhage.