Despite increasing experience and improved material, endovascular treatment of cerebral aneurysms still has risks linked to the technique itself and to the specificity of the pathology treated. The purpose of this report is to examine procedural technical and clinical negative events, even minimal ones, occurring in this type of treatment. We considered 557 procedures carried out from January 1994 to December 2005 in 533 patients harboring 550 aneurysms. Of the patients, 448 presented with SAH and 85 with unruptured aneurysms. All procedures were performed under general anesthesia. The GDC-10 system was routinely used. Additional devices like the balloon remodeling technique, Trispan and stents were also occasionally used. Every procedural complication occurring during or soon after treatment was registered. Endovascular treatment was completed in 539 out of 557 procedures. There were 18 failures (3.3%). Occlusion of the aneurysm was judged complete in 343 (64%), near complete in 184 (34%) and incomplete in 12 (2%). Procedural complications occurred in 72 (13%) of the cases. The most frequent negative events were thromboembolisms (6.6%) and ruptures (3.9%). Other types (coil migration, transient occlusions of the parent vessel, dissections and early rebleeding) were rarer (2.5%). In the majority of cases there were no clinical consequences. Procedural morbidity and mortality were 1.1 and 1.8%, respectively. Considering the 449 procedures performed in ruptured and the 90 in the unruptured aneurysms separately, morbidity and mortality were 1.1 and 2.2% in the former group and 1.1 and 0% in the latter. Many factors influence the risk of complications. Being progressively aware of this and with increasing experience, the frequency can be limited. Negative events linked to the procedure have more significant serious clinical consequences in patients admitted in a critical clinical condition after SAH, because of the already present changes involving the brain parenchyma and cerebral circulation.