We have implemented a virtual reality (VR) training system using head-mounted displays (HMD), which let the user immerse into the operating room. In this controlled environment, different approaches for aneurysm treatment can be explored for getting practice in head positioning and craniotomy. By changing the transparency of skull and brain and switching to the microscopic view, the intraoperative anatomy can be explored. The system offers several configurations of aneurysm and clips, so that different approaches can be trained.