The authors present a case of a child suffering from shunt-treated hydrocephalus and spastic quadriplegia who underwent surgery for placement of a baclofen pump. Magnetic resonance (MR) imaging performed prior to pump placement demonstrated no hindbrain herniation. Afterward, however, the patient exhibited symptoms of brainstem compression, and MR imaging revealed a significant Chiari I malformation along with a fully functioning ventriculoperitoneal shunt. Posterior fossa decompression was performed, and the patient's symptoms abated. The authors believe this to be the first report of an acquired Chiari I malformation in a patient with a baclofen pump. Clinicians should consider Chiari I malformation as a rare but severe complication of baclofen pump placement.