Most anterior communicating artery aneurysms arise in association with ipsilateral, dominant, proximal anterior cerebral artery(A1) segments and, as direct extensions of those vessels, are often somewhat directed toward the contralateral cerebral hemispheres. We classified the directions of the anterior communicating artery aneurysms based on three dimensional orientations of neck orifices and fundus projections which were then described schematically to demonstrate spatial orientations. We also analyzed 32 cases of anterior communicating artery aneurysm who had been operated on during recent 3.5 years according to this classification. Only the difference in the size of aneurysm in relation to the site of aneurysmal neck was statistically significant(p=0.0116), and there were no correlations between A1 hypoplasia and the site of aneurysmal neck, the projection of aneurysmal fundus and the size of aneurysm, and the intraoperative rupture and the projection of the aneurysmal fundus. Although meaningful clinical results could not be obtained, we believe this classification can be very helpful in planning traditional or endovascular surgeries for, and in understanding spatial directions of anterior communicating artery aneurysms.