Background <p>Chiari malformation type I (CM-I) is defined by downward herniation of the cerebellar tonsils through the foramen magnum, disrupting cerebrospinal fluid (CSF) flow and often associated with syringomyelia. The objective of this study was to evaluate the safety and clinical efficacy of posterior decompression and duroplasty using an autologous pericranial graft harvested through a separate skin incision.</p> Methods <p>This retrospective case series was conducted on 20 patients, aged 21–60, both sexes, diagnosed as CM-I, with and without syrinx, treated by suboccipital craniectomy, C1 laminectomy, minimal tonsillar coagulation, and duroplasty using pericranial graft harvested from separate skin incision. All patients were subject to complete neurological examination, headache was assessed using the Visual Analogue Scale (VAS). Radiological follow-up with magnetic resonance imaging (MRI) was performed at 3&#xa0;months and 1&#xa0;year after surgery.</p> Results <p>Suboccipital headache was present in 90% and upper limb numbness in 75%; 25% had syringomyelia. At 1-year follow-up, 95% of patients showed marked headache improvement, and 85–95% showed resolution of sensory and motor deficits. MRI demonstrated tonsillar rounding in 18 patients and major enlargement of retro- and subtonsillar CSF spaces in 17 cases. Neither CSF leaks nor meningitis was encountered in this study. One patient developed superficial wound infection that resolved with antibiotics and daily dressing.</p> Conclusion <p>Posterior fossa decompression with expansile duroplasty using a separately harvested autologous pericranial graft is a safe and effective technique for CM-I, providing favorable clinical and radiological outcomes with minimal complications.</p>