Objective To investigate the relationship between the dome direction of the anterior communicating artery aneurysm （ACoAA） and the geometric morphology of anterior cerebral artery A1 segment. Methods The digital subtraction angiography and clinical data of the patients with ACoAA were coⅡected retrospectively. According to the dome direction of the aneurysms, the ACoAA were divided into 5 types： anteroinferior direction, anterosuperior direction, posterosuperior direction, posteroinferior direction, and complex direction. According to the geometric morphology, the anterior cerebral artery A1 segment could be divided into ＂arc＂ pattern （type I a： convex shape, type I b： concave shape）, ＂S＂ pattern （type li a： inverse lateral ＂S＂ shape, type lib： lateral ＂S＂ shape）, ＂approximate straight line＂ pattern （type ma： downward sloping ＂approximate straight line＂ shape, type Ⅲb： upward-sloping ＂approximate straight line＂ shape, type Ⅲc： horizontal ＂approximate straight line＂ shape） and non-development pattern. Results A total of 200 patients with ACoAA were enroⅡed in the study, 93 in anterosuperior direction, 76 in anteroinferior direction, 8 in posteroinferior direction, 8 in posterosuperior direction, and 15 in complex direction. The geometric morphology of the anterior cerebral artery A1 segnent was as foⅡows： type I a （113 sides）, type I b （8 sides）, type Ⅱa （27 sides）, type lib （70 side）, type Ⅲa （21 side）, type Ⅲb （46 sides）, type Ⅲc （60 sides）, and nondevelopment （55 sides）. The dome direction of the ACoAAwas significantly correlated with the geometric morphology of the anterior cerebral artery A1 segnent in the dominant developing side 0（2 = 215. 582, P = 0. 000; Pearson contingency coefficient C was 0. 665, P =0. 000）. The dome direction of the ACoAA was not sifffificantly correlated with geometric morphology of the anterior cerebral artery A1 segnent in the non-dominant developing side 0（2= 5. 525, P = 0. 478）. When the ACoAA dome directed downward, the general performances of the A1 segment of the dominate developing side were type I a, type Ⅱ a or type Ⅲa. When the ACoAAdome directed upward, the ~neral performances of the A1 segnent of the dominate developing side were type I b, type IIb or type rob. When the dome direction of the ACoAA was a complex one, the A1 seffnent of the dominate developing side might had different morphologies. Conelusiom There is significant correlation between the dome direction of the ACoAA and the morphology of anterior cerebral artery A1 segments of the dominate developing side.