Abstract: Objective To explore the effect of extra-arachnoidal limited craniocervical bony decompression with extended duroplasty（ELBDED）on ChiariⅠdeformity in adults without local adhesive arachnoiditis. Methods Thirty-two adult patients with ChiariⅠdeformity,admitted to our hospital from July 1997 and August 2007,were retrospectively analyzed.Of the 32 patients,21 were complicated by syringomyelia but had no history of intracranial infection.The patients underwent ELBDED in combination with extended duroplasty.No arachnoid adhesion was found during operation.Arachnoid membrane was intact in 29 patients.Critical herniation of cerebellar tonsil,found in 3 patients,was aspirated through the dura mater. Results Of the 28 patients who were followed up for a mean time of 4.5 years（range 0.5-10.3years）,23（82.1%）had improvements in neurological disturbances,5 became stable with no exacerbation of the disease.Seventeen patients with syringomyelia underwent MR imaging.The syrinx became smaller or collapsed in 15 patients,and remained stable in 2 patients.Postoperative complications including subcutaneous hydrocele and acute hydrocephalus occurred in 2 cases,respectively,after the arachnoid was opened.The complications disappeared after lumbar and ventricular drainage. Conclusion Long time good results can be achieved in ChiariⅠdeformity adult patients without local adhesive arachnoiditis with ELBDED.