STUDY DESIGN: Systematic literature review plus expert opinion framed on Delphi method. OBJECTIVE: To analyze the influence of coexistent Chiari I Malformation (CMI) on the management of Basilar Invagination (BI). SUMMARY OF BACKGROUND DATA: Basilar Invagination (BI) and Chiari 1 Malformation (CMI) constitute the commonest anomalies of the cranio-vertebral junction (CVJ). Treatment becomes even more challenging for patients in whom both pathologies co-exist. METHOD: Using PubMed, the authors identified 48 publications published between 2011 and 2022 concerning the incidence and management of both pathologies in combination. By means of the Delphi method, a panel of expert spine surgeons analyzed the strength of the published literature and voted statements concerning the management of BI combined with CMI. RESULT: The incidence for a combination of BI with CMI is estimated between 2.4/100000 in children and 9.6-19.7/100000 in adults. BI with ventral compression of the medulla related to AAD can be treated in a single operation by sagittal realignment via C1-C2 facet joint distraction and fusion. In the event of unreducible BI, insufficient ventral decompression by C1/2 fusion alone may be overcome by adding a foramen magnum decompression to allow posterior shift of the medulla. BI patients with concomitant CMI have an undersized posterior fossa volume This implies that surgical treatment of BI combined with CMI has either to increase posterior fossa volume or to include a posterior decompression. CONCLUSION: In patients with BI, concomitant CMI is a modifier of surgical management. In BI with AAD, an additional foramen magnum decompression should be added to posterior C1-C2 realignment and fusion. In BI without AAD, whether treatment is restricted to FMD or C1/2 fusion is required on top or alternatively, demands further studies. Odontoid resections are reserved for patients with insufficient alignment after posterior surgery.