OBJECTIVES: Supraorbital route through eyebrow incision, mini-pterional craniotomy, and midline interhemispheric route are most generally used methods for key hole surgery on anterior circulation aneurysm. Surgical route is determined according to aneurysm architecture and patient status. The approaching route can be selected according to the findings of 3-dimensional computed tomography (CT) angiography simulation. Prospective decision-making protocol, surgical technique of key hole surgery, and the results are presented in this paper. METHODS: 173 patients with anterior circulation aneurysms were treated by direct surgical neck clipping during last two years. Twenty patients of poor grade (Hunt-Hess grade IV,V) were treated by craniectomy with clipping. Decision making protocol was applied to 153 unruptured and good grade ruptured aneurysm patients. Simulation of key hole surgery was conducted by CT work station using conventional software InSpace (Siemens, Germany), and direction and shape of aneurysm was observed from the perspective of microsurgery. RESULTS: 113 ruptured and 40 unruptured aneurysms were secured through one of the three approaching routes. Supraorbital approach had been performed in 82 cases (unruptured 24, ruptured 58) while 64 cases were treated by mini-pterional craniotomy. Midline key hole surgery were carried out in seven distal anterior circulation aneurysms (DACA) using brain navigation system. After locating the aneurysm, supraorbital approach was applied to 46 cases involving anterior cerebral artery (ACA), 16 in internal carotid artery (ICA) and 20 in middle cerebral artery (MCA). Mini-pterional craniotomy was carried out in aneurysms located in ACA (9), ICA (18), and MCA (37). In most cases, the results of clipping were good. The average follow-up time was 16.7months (ranging 2 to 32months) and the results were cosmetically excellent. CONCLUSION: Simulating surgical approaches with 3-D CT angiography is a highly useful method for determining various surgical routes in anterior circulation aneurysm treatment. Therefore, minimally invasive and tailored surgical approaches are recommended since optimal route can be found through simulation. Thus, minimal invasive and tailored surgical approach is available through this method. These procedures have clear advantages; shorter surgical time and hospital stay, less operative trauma, reduced costs and less pain, and better cosmetic outcomes compared to standard craniotomy. Optimal surgical results are expected from minimally invasive and tailored surgical craniotomy.