PURPOSE: To report a causal relationship between Chiari I malformation and its rare, but recognized manifestation of bilateral papilledema. DESIGN: Interventional case series. METHODS: Four adult female patients (mean age, 48, age range 25-59 years) with bilateral papilledema, signs and symptoms of increased intracranial pressure, and cranial magnetic resonance imaging (MRI) evidence of a Chiari I malformation ranging from 7 to 22 mm of tonsillar herniation underwent suboccipital decompression. RESULTS: In all four patients, suboccipital decompression was followed by resolution of bilateral papilledema and signs and symptoms of increased intracranial pressure. CONCLUSION: Patients with bilateral papilledema and presumed pseudotumor cerebri require a cranial MRI to determine if they have a Chiari I malformation, because patients with increased intracranial pressure and papilledema from a Chiari I malformation may benefit from suboccipital decompression. © 2002 by Elsevier Science Inc. All rights reserved.