Background: A halo vest is an immobilization device widely used to stabilize the cervical spine. Pain and infection at the skull pin insertion site are common complications, but skull perforation is rare, and most published studies are case reports. This study aimed to identify risk factors for skull perforation by comparing patients who did and did not develop perforation.Methods: Overall thickness and the thicknesses of the internal and external laminae of the skull at the skull pin insertion sites were measured on cranial computed tomography scans of 66 patients fitted with a halo vest. The results were compared between patients who did and did not develop perforation.Results: Four patients developed perforations. All patients with perforation were older women, and their external and internal laminae were significantly thinner than those of patients who did not develop perforation.Conclusion: The reported causes of skull pin perforation include infection around the pin, osteoporosis, and an enlarged frontal sinus. However, most patients with perforation in the present study were older women, and the cause was the thinning of the external and external laminae.