BACKGROUND AND PURPOSE: Hostile hemodynamic conditions and geometries are thought to predispose aneurysms for instability and rupture. This study compares stable, unstable, and ruptured aneurysms while controlling for location and patient characteristics. MATERIALS AND METHODS: The hemodynamics and geometries of 165 stable, 65 unstable, and 554 ruptured aneurysms were compared. Hemodynamics was modeled using image-based computational fluid dynamics. Case-control pairs were selected matching aneurysm location, patient age, and sex. Paired Wilcoxon tests were used to compare hemodynamic and geometric variables among different aneurysm groups. The pairing was repeated 100 times, and the combined P values were calculated and adjusted for multiple testing. RESULTS: Ruptured aneurysms had lower minimum wall shear stress (P =.03), higher maximum wall shear stress (P =.03), more concentrated (P =.03) and mean oscillatory shear stress (P =.03), higher maximum velocity (P =.03), and more complex flows (vortex core-line length, P=.03) than stable aneurysms. Similarly, unstable aneurysms had more concentrated shear stress (P=.04) and more complex flows (vortex core-line length, P =.04) than stable aneurysms. Compared with stable aneurysms, ruptured aneurysms were larger (size ratio, aneurysm size/vessel size, P =.03), more elongated (aspect ratio, P =.03), and irregular (nonsphericity index, P =.03). Similarly, unstable aneurysms were larger (size ratio, P =.04), more elongated (aspect ratio, P =.04), and irregular (bulge location, P =.04; area-weighted Gaussian curvature; P =.04) than stable aneurysms. No significant differences were found between unstable and ruptured aneurysms. CONCLUSIONS: Unstable and ruptured aneurysms have more complex flows with concentrated wall shear stress and are larger, more elongated, and irregular than stable aneurysms, independent of aneurysm location and patient sex and age.