Objective: Observe whether the suboccipital foramen magno decompression, duraplasty and microsurgery lyses of arachninodal bands are a safe and an effective treatment. Method: A retrospective study was carried out with 26 consecutives patients with CM1 malformations diagnosed, evaluated and operated at the Neurosurgical department of Servidores do Estado Hospital (HSE), from 1986 to 2010. The radiological studies, patient records, surgical descriptions, and when available, surgical videos, were reviewed, creating a database from which information pertinent to the present study was collected. The follow-up varied from 8 to 168 months (mean, 48 months). Results: Twenty-six patients underwent posterior fossa decompression with duraplasty. In this series, there is no operative death. We noticed beneficial outcome in 69.2% of patients, and 4 cases of transient postoperative complications. Conclusion: This experience with 26 cases CM1 proved that suboccipital craniectomy; duraplasty with autologus pericranium and microlysis of adhesions is a safe and effective procedure.