A brain aneurysm is a bulge in a blood vessel in the brain caused by a weakness in the blood vessel wall. Rupture causes subarachnoid haemorrhage, a subset of stroke with a poor prognosis. To prevent rupture, brain aneurysms can be treated preventively by neurosurgical treatment (clipping) or by an endovascular approach via the groin. In the first part of this thesis, we describe the current treatment risks of preventive aneurysm treatments. With a group of international aneurysm experts we developed two risk scores to better predict the risk of neurological complications. For this study, we collected data from 10 hospitals in Europe, North America, and Asia. Based on a combination of seven patient, aneurysm and treatment characteristics, the risk scores allow for a better individual assessment of the risk of complications. The treatment risks in our study are higher than in previous studies. This can be explained by differences in definitions. Earlier studies focused on complications with severe consequences (death or dependence), while we also included treatment complications causing non-permanent neurological deterioration. The second part of this thesis describes the quality-of-life (QoL) outcomes in patients with and without a preventive aneurysm treatment in the first year after diagnosis. We found that treated patients experienced more restrictions during their recovery period, but that their QoL gradually increased afterwards. For untreated patients, the greatest improvement in QoL occurred directly after visiting the aneurysm clinic. A passive coping style is the most important predictor of poor QoL outcomes in all aneurysm patients.