Aim. To establish the risk factors for complications and fatal outcome after the operative occlusion of cerebral aneurysms. Methods. Retrospective study on 91 (lethality rate) and on 72 operated patients (complications). For survived and dead patients, as well as for patients with and without complications, following parameters were compared: gender, age, clinical condition, preoperative interval, use of temporary clips, vasospasm, outcome, as well as localization, size and intraoperative rupture of the aneurysm. Results. Complications existed: in 54.5% of aneurysms of middle cerebral and 13.6% of aneurysms of internal carotid artery (p<0.01); in 18.2% of patients in the first and 45.8% of patients in the third clinical Hunt and Hess group (p<0.05); in 57.9% of patients with and 20.5% of patients without intraoperative rupture (p<0.01); in 50% of patients with and 18.7% of patients without vasospasm (p<0.05). Average aneurysmal size was 18 mm in group with complications and 10.8 mm in patients with no complications (p<0.05), while average preoperative intervals in these two groups were 20 and 8.7 days (p<0.05). Lethality rate was 25% for the third and 83.3% for the fourth and fifth clinical group (p<0.01), and the existence of complications significantly increased mortality (from 15.7% to 50%, p<0.01). Good outcome existed in 19.2% of operated patients with complications and in 78.3% of those without complications (p<0.01). Conclusions. Incidence of complications depended significantly on preoperative clinical condition, duration of preoperative interval, size, localization and intraoperative rupture of aneurysm. Complications significantly minimized the surgical treatment outcome and increased the lethality rate mortality.