We examined cases in which cerebral aneurysms ruptured during the follow-up period. From 1993 to 2010, we encountered 14 such cases, and the mean age of the patients was 62.6 years (age range, 39–81 years; M: F＝8: 6). Nine cases were incidental, three were associated with ruptured aneurysms and two were symptomatic. Five cases involved the anterior communicating artery (A-com); four, the middle cerebral artery; three, the internal carotid artery; and two, the basilar artery. The size of the aneurysm at diagnosis ranged from 1 to 33 mm, and 50% of the aneurysms were smaller than 5 mm; moreover, 80% of the A-com aneurysms were smaller than 3 mm. The mean latency period to rupture was 22.3 months (ranged 13 days to 53 months), and in five cases (35%), the ruptures occurred within one year. Seven patients who had World Federation of Neurological Surgeons (WFNS) Grade I–IV hemorrhage survived after discharge, while seven patients of WFNS Grade V died. In nine patients in whom the morphological change could be assessed, the mean growth rate of the size of the aneurysm was 1.9. In our study, many of the ruptures occurred in the early years of the follow-up, and this suggests that the interval of follow-up with 3D-CTA or MRA should be shorter in the early period after aneurysm detection.