BACKGROUND: Chiari malformations type I are commonly encountered in pediatric patients. Posterior fossa decompression with or without duraplasty is recommended for patients with intractable symptoms, as well as those showing evidence of brainstem dysfunction. OBSERVATIONS: In this report, the authors describe the case of a 19-year-old female who presented to the neurosurgery clinic with delayed synthetic dural graft breakdown as well as associated pseudomeningocele and intracranial hypotension. She underwent exploration and revision of her duraplasty, where a dural defect measuring 1.5 cm in diameter was observed. The defect was not contiguous with peripheral sutures. The defect was repaired with a pericranium autograft and reinforced with dural sealants. Her postoperative course was complicated by scalp dysesthesia. LESSONS: To the authors' knowledge, this is the first reported case of a synthetic dural graft breakdown following posterior fossa decompression with duraplasty. https://thejns.org/doi/10.3171/CASE24715.