Although three-dimensional computed tomographic angiography (3D-CTA) is less complicated and time-consuming than conventional cerebral angiography (CCA) and represents a reliable alternative for evaluating cerebral aneurysms, some patients experience aneurysmal rerupture during 3D-CTA. Two women, 79 and 71 years old, who presented with severe subarachnoid hemorrhage (SAH) underwent 3D-CTA within 3 h after SAH onset. Their images clearly indicated extravasation from their aneurysms. Neither patient recovered from deep coma, and both died within 2 days. We reviewed the literature with special reference to the condition of SAH patients at admission and the interval between SAH onset and 3D-CTA, and discuss serious complications of 3D-CTA study. Although aneurysmal rerupture may reflect the natural course, rerupture during 3D-CTA, especially in SAH patients who are in poor clinical condition during the acute stage, should be recognized as a potentially fatal complication. Their blood pressure must be strictly controlled and factors such as their clinical condition and the interval from the ictus must be considered.