A growing number of children and adolescents are being diagnosed as Chiari malformation type Ⅰ (CM-Ⅰ) for behavioral disorders,developmental delay,seizures,or abnormal orpharyngeal function.The aim of this study was to compare the clinical characteristics,imaging findings and surgical outcomes of CM-Ⅰ in pediatric and adult patients.Between January 2014 and June 2017,84 patients with CM-Ⅰ underwent surgical treatment in our department.We divided the patients into two groups:pediatric group (n=1 1,age ＜18 years)and adult group (n=73,age ≥18 years).Data on clinical characteristics,imaging findings,surgical outcomes,and prognosis were retrospectively reviewed and compared between these two groups.For clinical presentation,scoliosis (36.4％) and developmental delay (36.4％) were more common in pediatric patients,whereas,sensory disturbance (58.9％) and motor weakness (41.1％) were more common in adult patients.Imaging findings showed that the incidence of hydrocephalus and craniovertebral junctional abnormalities was significantly higher in pediatric group than in adult group (P＜0.05).Compared to adult group,pediatric group showed a better improvement or resolution of syrinx and tonsillar hiation after surgical treatments (P＜0.05).The total Chicago Chiari Outcome Scale (CCOS) score in pediatric patients at the last follow-up was significantly higher than that in adult patients (P=0.002).In conclusion,the clinical characteristics and imaging findings appeared to be different in pediatric and adult patients with CM-Ⅰ.The surgical outcomes of pediatric patients were shown to be significantly better than those of adult patients.