Treatment of complex intracranial aneurysms by means of interventional neurovascular techniques is now being performed with a newly developed silicone detachable-microballoon device. The balloon is composed of unique silicone elastomers that are extremely soft and malleable. It therefore conforms to the blood vessel lumen or aneurysm wall and reduces the risk of rupture. It is affixed onto a 2.0-F catheter and can be either directed by flow or guided with the catheter. For aneurysms with a well-defined neck, the balloon is placed directly into the aneurysm, inflated with 2-hydroxyethyl methacrylate for permanent solidification, and detached. The aneurysm is thus excluded from the circulation, and the parent vessel is preserved. For aneurysms without a well-defined neck, test occlusion can be performed, followed by permanent balloon occlusion of the parent vessel. This balloon technique has been successfully used to treat aneurysms in both the anterior and posterior circulations, where standard neurosurgical techniques have failed, and in surgically inaccessible anatomic locations.