BACKGROUND The size of the saccular intracranial aneurysm (IA) has been used as the primary indicator for rupture risk. We investigated at which size IAs that rupture did so, and whether this size has significantly changed over time. METHODS Patients treated for ruptured IAs were identified from the Aneurysm Database of the Tampere University Hospital. The size of the IA at the time of rupture was measured from computed tomographic angiography or digital subtraction angiography made to diagnose the aneurysm. Data for the clinical risk factors for rupture were collected from the patient's medical records. RESULTS Of the 2545 patients with ruptured intracranial aneurysms (IAs) admitted, the size of the ruptured IA could be determined for 76% (1925 of 2545). Fifty‐one percent (984 of 1925) of the studied IAs ruptured at a size <7 mm. Both the mean and the median size of the IA at rupture had a downward trend from 1989 to 1997 (median decrease from 10 mm to 6 mm) but have remained relatively constant since. Forty‐six percent (881 of 1925) of the patients with a ruptured IA were not known to have any lifestyle‐related aneurysmal subarachnoid hemorrhage risk factor. Of the IAs that ruptured small, 35% were located in the anterior communicating artery and 14% in other small intracranial arteries. CONCLUSION Small size should not be used to exclude unruptured IAs from prophylactic treatment. The observation that the size at which IAs rupture has previously decreased, suggesting a change in relative importance of risk factors or characteristics of a contemporary patient population compared with older cohorts.

In a recent article published in Neurology, Rautalin et al.1 report substantial regional differences and a decreasing trend in the incidence of aneurysmal subarachnoid hemorrhage (aSAH) in all regions of Finland. However, in Tampere University Hospital, one of the referral centers for the population in this article, we do not see the decreasing trend in the number of admitted aSAH cases, but rather a constant variation from 1990 to 2014.2