OBJECTIVE: Detection of intracranial multiple aneurysms, including mirror-image aneurysms, have recently been increasing with the development of diagnostic techniques. However, studies of mirror-image aneurysms have been rare in South Korea. Thus, we intend to report our hospital's experience with mirror-image aneurysms during the past 20 years along with a review of relevant literature. METHODS: We analyzed medical records and image data from patients with cerebral aneurysms who had been admitted to our institution from January 1988 to June 2007. We divided the patients into three groups and investigated the clinical patterns of mirror-image aneurysms (Group 1). We then compared them with patients exhibiting non-mirror multiple aneurysms (Group 2) and the patients with solitary aneurysms (Group 3). We also statistically analyzed the age, sex, smoking habits, medical histories, and prognoses of the patients. RESULTS: Mirror-image aneurysms were found in 62 (5.1%) of the 1,209 patients admitted for cerebral aneurysms over the past 20 years. Of the mirror-image aneurysms, 48% were located in the posterior communicating artery (PcoA), and 40% were in the middle cerebral artery (MCA). Ruptures of aneurysms occurred slightly more frequently on the right side and when the aneurysm was larger and its shape was more irregular. Women, particularly menopausal women aged 50 and older, were shown to be at higher risk. Smoking was also a risk factor. However, there were no significant differences in prognoses among the three groups. CONCLUSION: We should pay attention to the possibility of mirror-image or multiple aneurysms when diagnosing and treating menopausal women and smokers, particularly if the cerebral aneurysm is located in the MCA or PcoA.