A 49-year-old man with syringomyelia and a Type I Arnold-Chiari malformation (Chiari-I) was diagnosed with growth hormone insensitivity syndrome (GHIS). He was short in stature, had high circulating levels of GH, and low circulating levels of insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3). His GH responses to the administration of growth hormone-releasing hormone (GHRH) and L-DOPA were normal, but his levels of IGF-I and IGFBP-3 did not increase after the administration of exogenous GH. Direct genomic DNA sequencing revealed neither a mutation nor deletion in this patient's GH receptor (GHR) gene, though one polymorphism was detected, indicating that his GHR gene was normal. This is the first reported case of an association of GHIS with syringomyelia and Chiari-I malformation.