To determine the significance of hypertension in the pathogenesis of berry aneurysms, 113 patients with subarachnoid haemorrhage (SAH) and verified aneurysm and 63 patients with SAH without aneurysm were compared. Of those patients with angiographically verified aneurysms, 61.9% were found to have elevated blood pressure (greater than 160/95 mmHg) and 19.5% showed electrocardiographic signs of left ventricular hypertrophy (SV1 + RV5 (6) greater than 3.5 mV). The percentages for patients without aneurysm were 36.5% and 6.4% respectively. A significant correlation was found between anterior aneurysms and left ventricular hypertrophy (P less than 0.01). The mean Sokolow index values were also significantly elevated in cases of aneurysm (P less than 0.01). There was a complementary relationship between the extent of left ventricular hypertrophy and the percentage of females with regard to localization of an aneurysm and age group. The predominance of females in the total aneurysm population, in the 50- to 59-year-old age group, and among patients with internal carotid aneurysms indicates that a sex-specific hormonal factor may also play a role in the pathogenesis of aneurysms in addition to hypertension. The collagen wasting commonly observed in bone and skin in the post-menopausal period due to decreased oestrogen levels could possibly be responsible for the formation of aneurysms in the proximal segments of the cerebral arteries, as occurs in various connective tissue diseases.