Purpose:To access the safety of low-dose heparin in comparison to a high-dose regimen in patients undergoing intracranial stent-assisted angioplasty. Methods: Sixty-four consecutive patients (53 men; mean age 54 years) undergoing stent-assisted angioplasty of 70 intracranial arterial stenoses were randomized to receive either low-dose (2000-U bolus+500 U/h) or high-dose (3000-U bolus+800 U/h) intravenous heparin during the procedure. The activated clotting time (ACT) was measured. The groups were compared for the following primary endpoints until hospital discharge: target lesion acute thrombosis, intracranial hemorrhage (ICH), and death. Results: The overall angioplasty success rate was 93% (65/70 lesions). Stents were placed in 94.7% (36/38) and 90.6% (29/32) of patients in the low-dose and high-dose groups, respectively (p=0.65). The primary endpoint occurred in 6% (2/33) of patients in the low-dose group versus 16% (5/31) of patients in the high-dose group (p=0.25). Two patients, 1 patient in each group, experienced acute target lesion thrombosis during the procedure (p=NS); ICH occurred in 5 patients: 1 in the low-dose group and 4 in high-dose group (3.0% versus 12.9%, p=0.19). Conclusion: The use of a low-dose heparin regimen did not increase the incidence of target lesion thrombosis or ICH in this small pilot trial. Intraoperative low-dose heparin seems to be safe for patients undergoing intracranial stent-assisted angioplasty, but these data should be confirmed in a larger trial. J Endovasc Ther. 2009;16:642-648