['Red blood cell transfusion (RBCT) may increase the risk of thrombotic events (TE) in patients with subarachnoid hemorrhage (SAH) through changes induced by storage coupled with SAH-related hypercoagulability. We sought to investigate the association between RBCT and the risk of TE in patients with SAH.', '205 consecutive patients with acute, aneurysmal SAH admitted to the neurovascular intensive care unit of a tertiary care, academic medical center between 3/2008 and 7/2009 were enrolled in a retrospective, observational cohort study. TE were defined as the composite of venous thromboembolism (VTE), myocardial infarction (MI), and cerebral infarction noted on brain CT scan. Secondary endpoints included the risk of VTE, poor outcome (modified Rankin score 3-6 at discharge), and in-hospital mortality.', '86/205 (42 %) received RBCT. Eighty-eight (43 %) had a thrombotic complication. Forty (34 %) of 119 non-transfused and 48/86 (56 %) transfused patients had a TE (p = 0.002). In multivariate analysis, RBCT was associated with more TE by [OR 2.4; 95 % CI (1.2, 4.6); p = 0.01], VTE [OR 2.3; 95 % CI (1.0, 5.2); p = 0.04], and poor outcome [OR 5.0; 95 % CI (1.9, 12.8); p < 0.01]. The risk of TE increased by 55 % per unit transfused when controlling for univariate variables. Neither mean nor maximum age of blood was significantly associated with thrombotic risk.'] Does red blood cell transfusion increase the risk of thrombotic events in patients with subarachnoid hemorrhage?