Flow diverters (FD), a new generation of intracranial stents with a low porosity mesh, have been applied as an alternative treatment for intracranial aneurysms. However, their efficacy varies among aneurysms of different morphology. In this study, computational fluid dynamic simulations were performed to examine the influence of an FD on the hemodynamics of wide-necked and narrow-necked cerebral aneurysms. An FD with 70% porosity mesh was deployed across the neck of an ideal narrow-necked and wide-neck aneurysm model. The hemodynamics at the aneurysmal sac were changed markedly in both models. At the inflow portion of the aneurysm neck of the narrow-necked aneurysm, the peak velocity and wall shear stress were reduced by 84% and 91%, respectively. By comparison, in the wide-necked aneurysm model, the results were 47% and 21%, respectively. This study demonstrates that the FD markedly altered the hemodynamic conditions inside intracranial aneurysms, depending on aneurysm morphology. Therefore, hemodynamic modifications should be individually designed for aneurysms with different morphology.