OBJECTIVE Intracranial arterio-venous malformations (AVM) often represent a complex clinical problem as regards indications to treatment, the choice of treatment and the technical difficulties related to treatment. In the last twenty years, endovascular treatment of intracranial arterio-venous malformations was primarily based on an acrylic glue (Hystoacril) whose endovascular use is not free from risks. A new product for endovascular embolization, named ONYX, has been recently been made commercially available. It is a bio-compatible liquid polymer that precipitates and solidifies in contact with blood, thus forming a soft and spongy embolus. The aim of this study was to evaluate our preliminary results in the endovascular embolization of intracranial AVM with Onyx. METHODS Ten patients were treated (7 men, 3 women; mean age: 29 years, range: 12-48 years) for a total of 37 embolizations, 22 with Onyx and 15 with acrylic resin. RESULTS Nidus occlusion was complete in 2 cases, >90% in 2 cases, >50 and <90% in 3 cases and <50% in the remaining 3 cases. The following complications were recorded: two transient and one mild permanent neurological deficits, two clinically silent cases of moderate subarachnoid haemorrhage, four catheters glued to the injection site, three cases of treatment discontinuation due to continuous and massive reflux of Onyx into the afferent artery peduncle. CONCLUSIONS This early experience showed that while Onyx has good embolization potential it also presents some disadvantages, which need to be overcome before this product can be considered easy and safe to use on a large scale.