Object. Use of the Onyx liquid embolic system has become in option for treating chiral arteriovenous fistulas (DAVFs) because of its advantageous nonadhesive and cohesive properties. However. the complication rates associated with the use of this system have not been reported. The authors present their initial experience of the risks related to transarterial embolization using this system. Methods. Between February 2005 and February 2007, 31 patients with DAVFs were treated at Beijing Tiantan Hospital. Transarterial embolization using Onyx-18 was performed as a preoperative adjunct or as definitive therapy. The demographic characteristics, angiographic features. clinical presentation, treatment, and outcome of the patients were reviewed. Clinical follow-up status was suplemented by telephone interviews to determine Glasow Outcome Scale scores. Results. In 19 patients (61.3%) there was complete angiographic evidence of elimination of the shunts and resolution of the symptoms. The remaining 12 patients were treated successfully but did not attain complete embolization and had residual shunting. Adverse events Occurred in 5 of 3 1 patients, with 3 DAVFs located at the tentorium, I at file inferior petrosal sinus. and I at the cavernous sinus. Complications included trigeminocardiac reflex in 2 patients (6.5%), hemifacial hypesthesia in 3 patients (9.7%). hemifacial palsy in 2 patients (6.5%), jaw pain in 1 patient (3.2%), posterior fossa infarction in 1 patient (3.2%), and microcatheter gluing in 1 patient (3.2%). At the last follow-up examination. all patients had returned to all independent clinical Status. Conclusions. Although a complete resolution of symptoms can be achieved Mill transarterial embolization using the Onyx liquid embolic system. the potential for serious complications exists with this procedure, necessitating the participation of a skilled neurointerventionalist. (DOI: 10.3171.JNS.2008.109.12.1083)