OBJECTIVE In Chiari malformation type I (CM-I), a variety of imaging findings have been purported to be important; however, results have been inconclusive, inconsistent, or not replicated in independent studies. The purpose of this study was to report imaging characteristics for a large cohort of patients with CM-I and identify the imaging findings associated with surgical decompression. METHODS Patients were identified using ICD-9 codes for CM-I for the period from 1996 to 2017. After review of the medical records, patients were excluded if they 1) did not have a diagnosis of CM-I, 2) were not evaluated by a neurosurgeon, or 3) did not have available preoperative MRI. Retrospective chart review was performed to collect demographic and clinical data. Imaging parameters were measured according to the Chiari I Malformation Common Data Elements. RESULTS A total of 731 patients were included for analysis, having a mean follow-up duration of 25.5 months. The mean age at presentation was 8.5 years. The mean tonsil position was 11.4 mm below the foramen magnum, and 62.8% of patients had a pegged tonsil shape. Two hundred patients (27.4%) underwent surgery for life-dominating tussive headache, lower cranial nerve dysfunction, syrinx, and/or brainstem dysfunction. Surgical treatment was associated with a syrinx (OR 20.4, 95% CI 12.3-33.3, p < 0.0001), CM-1.5 (OR 1.797, 95% CI 1.08-2.98, p = 0.023), lower tonsil position (OR 1.130, 95% CI 1.08-1.18, p < 0.0001), and congenital fusion of cervical vertebrae (OR 5.473, 95% CI 1.08-27.8, p = 0.040). Among patients with benign CM-I, tonsil position was statistically significantly associated with future surgery. CONCLUSIONS Comprehensive imaging characteristics for a large cohort of patients with CM-I are reported. Analysis showed that a lower tonsillar position, a syrinx, and CM-1.5 were associated with undergoing posterior fossa decompression. This study demonstrates the importance of considering imaging findings in the context of patient symptomatology.