Inclusion Criteria:

• Patient must be 18-75 years of age at the time of screening.
• Patient must have a single ruptured or unruptured IA (intracranial aneurysm) requiring treatment.  If the subject has an additional IA requiring treatment, the additional IA must not require treatment within 60 days of the index procedure.
• For the purposes of this study a ruptured IA patient is defined as a patient with computed tomography (CT), magnetic resonance imaging (MRI), or lumbar puncture (LP) evidence of subarachnoid hemorrhage attributed to the index aneurysm within the last 60 days.
• The index IA to be treated must have the following characteristics:
  • Saccular in shape;
  • Located in basilar apex (BA), middle cerebral artery (MCA) bifurcation, internal carotid artery terminus (ICAt), anterior communicating artery complex (ACom);
  • Dome-to-Neck (DN) ratio ≥ 1;
  • Diameter of the IA is appropriate for treatment with the WEB Aneurysm Embolization System per device Instructions for Use;
  • Wide-neck IA with neck size ≥ 4mm or Dome-to-Neck (DN) < 2.
• Patient has an IA that is appropriate for treatment with WEB without the use of additional implanted devices.
• If the IA previously ruptured, patient must be neurologically stable with Hunt & Hess Score of I or II.
• Patient must be able to comply with all aspects of the screening, evaluation, treatment, and the post-procedure follow-up schedule.
• Patient must sign and date an IRB/EC-approved written informed consent prior to initiation of any study procedures.

Exclusion Criteria:

• Patient has an IA with characteristics unsuitable for endovascular treatment.
• Microcatheter could not reach patient’s index aneurysm to allow necessary access to treat with study device.
• Patient has vessel characteristics, tortuosity or morphology which could preclude safe access and support during treatment with study device.
• Patient has vascular disease or other vascular anomaly so as to preclude the necessary access to the aneurysm for use of the study device.
• Patient has clinical, angiographic or CT evidence of vasospasm, vasculitis, an intracranial tumor (except small meningioma) or any other intracranial vascular malformations on presentation.
• Patient has conditions placing them at high risk for ischemic stroke or has exhibited ischemic symptoms such as transient ischemic attacks, minor strokes, or stroke-in-evolution within the prior 60 days.
• Patient has any circulatory, neurovascular, cardiovascular, or neurologic conditions that have resulted in unstable neurological symptoms.
• Patient has mRS ≥ 2 prior to presentation or rupture (as applicable).
• Patient has had an SAH from a nonindex IA or any other intracranial hemorrhage within 90 days.
• Patient has physical, neurologic or psychiatric conditions which preclude his/her ability to comply with all aspects of the screening, evaluation, treatment, and the postprocedure follow-up schedule.
• Patient’s index IA was previously treated.
• Patient is taking anticoagulants or has a known blood dyscrasia, coagulopathy, or hemoglobinopathy.
• Patient is pregnant.
• Patient has known hypersensitivity, which cannot be medically treated, to any component of the study device, procedural materials, or medications commonly used during the procedure.
• Patient is concurrently involved in another investigational study or a postmarket study that could affect the safety and effectiveness of IA treatment with the study device or with the study’s follow-up schedule.
• Patient has an acute life-threatening illness other than the neurological disease to be treated in this trial.
• Patient has a life expectancy of less than 5 years due to other illness or condition (in addition to an intracranial aneurysm).