Background and purpose The risk factors for adverse events for example, intraprocedural rupture (IPR), ischemic complication within 24 hours, and rebleeding after endovascular coil embolization for a ruptured cerebral aneurysm remain unclear. The aim of this study was to identify significant associated risk factors.

Methods We retrospectively evaluated data from 5358 patients listed on the Japanese Registry of Neuroendovascular Therapy 3 during 2010–2014.

Results IPR, ischemic complications, and rebleeding occurred during or after 221 (4.1%), 226 (4.2%), and 63 (1.2%) treatments, respectively. All of the adverse events were significantly associated with the patients’ poor outcomes at 30 days. Multivariate analysis revealed the factors independently related to these adverse events as follows: (1) for IPR: female sex, bifurcation type, <5 mm aneurysm, emergent surgery, local anesthesia, a balloon-assisted technique; (2) for an ischemic complication: poor World Federation World Federation of Neurological Societies (WFNS) grade, wide neck, and stent-assisted technique; (3) for rebleeding: poor WFNS grade, bifurcation type, wide neck, and body filling as the initial result.

Conclusions Knowledge of the risk factors of endovascular coil embolization and paying attention to them are essential for patients’ safe treatment and good outcomes.