To identify clinical and morphologic risk factors correlated with anterior communicating artery (ACoA) aneurysm formation. Three-dimensional morphologic parameters obtained from computed tomography angiography or digital subtraction angiography from 504 patients with ACoA aneurysms and 201 patients with aneurysms in other locations that were diagnosed at Brigham and Women's Hospital and Massachusetts General Hospital between 1990 and 2016 were evaluated. The presence of hypoplastic and aplastic A1 segments and diameters and angles of surrounding parent and daughter vessels were examined. Univariable and multivariable statistical analyses were performed to determine statistical significance. Sensitivity analyses for small (≤3 mm) aneurysms only were also performed. Aplastic and hypoplastic A1 segments were more common in the ACoA group (38.9% vs. 6.5% hypoplastic and 22.2% vs. 0.5% aplastic). In multivariable analysis, the presence of a hypoplastic A1 segment was associated with ACoA aneurysms. An A2-ACoA (daughter-daughter) angle was also significantly associated with ACoA aneurysms in multivariable analysis; however, as Pearson's correlation test between aneurysm width and daughter-daughter angle was significant, the daughter-daughter angle was most likely not independently associated with aneurysm presence, but rather might have been a result of the presence of an aneurysm. Subgroup analyses of small aneurysms (≤3 mm) and of unruptured aneurysms showed similar results. Our results demonstrate that of all the morphologic parameters, the presence of a hypoplastic A1 segment was the only parameter independently associated with the presence of ACoA aneurysms that was not correlated with aneurysm size and could aid as a simple screening parameter.