Percutaneous embolization using detachable balloons was successfully performed in a series of nine patients with intracranial carotid aneurysms. The clinical progress and the results of MR examination are reported. Up to 4 months after treatment, MR imaging did not show any significant change in size of the artificially thrombosed aneurysms. Complete resorption cannot be expected in less than 6-8 months, but resorption does eventually occur. The intensity pattern observed in the evolution of the thrombus was similar to that of intra- and extra-cranial hematomas.