Objective Arterial hypertension (HTN) is a risk factor for subarachnoid haemorrhage (SAH). We aimed to assess the impact of premorbid HTN on the severity of initial bleeding and the risk of aneurysm rebleeding after SAH.

Design Retrospective analysis of a prospective cohort study of all SAH patients admitted to Columbia University Medical Center between 1996 and 2012.

Results We enrolled 1312 consecutive patients with SAH; 643 (49%) had premorbid HTN. Patients with premorbid HTN presented more frequently as Hunt–Hess Grade IV or V (36% vs 25%, p<0.001) and World Federation of Neurosurgical Societies (WFNS) Grade 4 or 5 (42.6% vs 28.2%, p<0.001), with larger amounts of subarachnoid (Hijdra Sum Score 17 vs 14, p<0.001) and intraventricular blood (median IVH sum score 2 vs 1, p<0.001), and more often with intracerebral haemorrhage (20% vs 13%, p=0.002). In multivariate analysis, patients with premorbid HTN had a higher risk of in-hospital aneurysm rebleeding (11.8% vs 5.5%, adjusted OR 1.67, 95% CI 1.02 to 2.74, p=0.04) after adjusting for age, admission, Hunt–Hess grade, size and site of the ruptured aneurysm.

Conclusions Premorbid HTN is associated with increased severity of the initial bleeding event and represents a significant risk factor for aneurysm rebleeding. Given that aneurysm rebleeding is a potentially fatal—but preventable—complication, these findings are of clinical relevance.