OBJECT: The authors hypothesized that children with preoperative Chiari I malformation and an absent gag reflex may harbor pharyngeal musculature atrophy identifiable on magnetic resonance (MR) imaging. METHODS: Thirty patients with preoperative Chiari I malformation and a functioning gag reflex, five patients with preoperative Chiari I malformation and complete absence of gag reflex, and 50 control individuals underwent radiological measurement of the posterior pharyngeal wall thickness. The thickness of the posterior pharyngeal wall in age-matched controls was significantly thinner (p < 0.0001) than that in patients with Chiari I malformation and no functioning gag reflex. Additionally, in patients with hindbrain herniation and absent gag reflex, the posterior pharyngeal wall thicknesses were comparable to or thinner than those in age-matched controls. A general decrease in the thickness of the posterior pharyngeal wall was found in control individuals who were older compared with patients with Chiari I malformation and a preserved gag reflex in whom the prevertebral soft tissues were found to increase in thickness with age. Analysis of these data showed that in children with a nonfunctioning gag reflex the prevertebral soft tissue, composed primarily of the superior constrictor muscle, is statistically thinner compared with that in age-matched controls and age-matched children with Chiari I malformation and a functioning gag reflex. The authors theorize that the discrepancy between this measurement in controls and patients with hindbrain herniation is due to the thickening of the craniocervical ligaments that is known to occur in this clinical entity. CONCLUSIONS: The finding that prevertebral soft tissue thickens with age in patients with Chiari I malformation and functioning gag reflex alone may aid in the interpretation of soft-tissue injury following cervical spine injuries in this group.