Percutaneous transluminal angioplasty for treatment of intracerebral arterial vasospasm is now being performed in selected cases. Thirty-six vascular territories in 13 patients, ranging in age from 15 to 73 years, have been treated with a new silicone microballoon device. This balloon has allowed mechanical dilatation of segmental and diffuse areas of spastic intracerebral blood vessels less than 1 mm in diameter with return to normal luminal diameter. Follow-up angiography has documented improved cerebral perfusion without return of spasm. In 10 patients (77%), vasospasm was due to subarachnoid hemorrhage following rupture of an intracranial aneurysm. In three patients (23%), spasm with resultant neurological decline occurred during detachable balloon embolization therapy for treatment of an aneurysm. In each case, the vessel caliber returned to normal size following balloon dilatation. In nine (69%) of the 13 cases, balloon dilatation resulted in improvement of neurological function within minutes to hours following the procedure. Transluminal angioplasty techniques may offer an alternative form of therapy in the management of symptomatic arterial vasospasm.