Four carotid-ophthalmic aneurysms were treated through a contralateral pterional approach. Three of these aneurysms were clipped successfully. Because awareness of the size and shape of the optic chiasm is crucial for the success of this approach, we used metrizamide or blood cisternography with a high resolution computed tomographic scanner. With this technique, the shape of the optic chiasm was delineated before operation to make certain that the prechiasmatic space was large enough for the aneurysm to be approached.