BACKGROUNDANDPURPOSE: Different hemodynamic patterns have been associated with aneurysm rupture. The objective was to test whether hemodynamic characteristics of the ruptured aneurysm in patients with multiple aneurysms were different from those in unruptured aneurysms in the same patient. MATERIALS AND METHODS: Twenty-four mirror and 58 ipsilateral multiple aneurysms with 1 ruptured and the others unruptured were studied. Computational fluid dynamics models were created from 3D angiographies. Case-control studies of mirror and ipsilateral aneurysms were performed with paired Wilcoxon tests. RESULTS: In mirror pairs, the ruptured aneurysm had more oscillatory wall shear stress (P<.007) than the unruptured one and tended to be more elongated (higher aspect ratio), though this trend achieved only marginal significance (P < .03, 1-sided test). In ipsilateral aneurysms, ruptured aneurysms had larger maximum wall shear (P<.05), more concentrated (P<.001) and oscillatory wall shear stress (P< .001), stronger (P<.001) and more concentrated inflow jets (P<.001), larger maximum velocity (P<.001), and more complex flow patterns (P<.001) compared with unruptured aneurysms. Additionally, ruptured aneurysms were larger (P<.001) and more elongated (P<.001) and had wider necks (P < .001) and lower minimum wall shear stress (P< .001) than unruptured aneurysms. CONCLUSIONS: High wall shear stress oscillations and larger aspect ratios are associated with rupture in mirror aneurysms. Adverse flow conditions characterized by high and concentrated inflow jets; high, concentrated, and oscillatory wall shear stress; and strong, complex and unstable flow patterns are associated with rupture in ipsilateral multiple aneurysms. In multiple ipsilateral aneurysms, these unfavorable flow conditions are more likely to develop in larger, more elongated, more wide-necked, and more distal aneurysms.