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More than 100 years after its identification, type I Chiari malformation remains poorly understood. Despite impressive advances in clinical diagnosis, neuroradiology, and neurosurgery, central questions about the pathogenesis, natural history, and prevalence of this condition remain unanswered. Although not common, Chiari malformation should be considered in any patient with signs and symptoms localized to the brain stem or cerebellum, particularly if signs and symptoms coexist with headache and signs of central cord involvement. More importantly, tonsillar ectopia always must be considered in the context of a thorough history and patient evaluation, with recognition that even patients with significant degrees of tonsillar ectopia may remain asymptomatic for extended periods. Craniocervical decompression is the preferred surgical treatment in most cases of type I Chiari malformation with or without syringohydromyelia.