The authors describe the off-label use of Onyx for embolization of fusiform mycotic and dissecting intracranial aneurysms based on their experience with 3 patients treated at the University of Utah Hospital from 2006 through 2007. Technical success in occluding the parent artery/aneurysm was achieved in all patients. There were no complications. The authors conclude that Onyx can be used to achieve occlusion of fusiform mycotic and dissecting intracranial aneurysms in conjunction with parent artery occlusion.