It is unclear if avoiding hyperglycemia during intensive care after acute brain injury improves morbidity, mortality, and neurologic outcome. This prospective randomized trial tested whether intensive insulin therapy affected infection rates, vasospasm, mortality, or long-term neurologic outcome in subarachnoid hemorrhage patients during their intensive care unit (ICU) stay. Comparison was made against conventional insulin therapy using a randomized trial design. The primary outcome measure was infection rate until the fourteenth postoperative day in the ICU or until patient discharge. Secondary end points were the incidence of vasospasm until the fourteenth postoperative day in the ICU or until patient discharge, and neurologic outcome and mortality at 6 months follow-up. A total of 78 patients were prospectively enrolled and randomly assigned either to conventional insulin therapy or to intensive insulin therapy (38 and 40 patients, respectively). The infection rate during the study was significantly higher in patients who received conventional insulin therapy than in patients who received intensive insulin therapy (42% vs. 27%; P<0.001). The incidence of vasospasm during the study was also similar in conventional and intensive therapy groups (31.5% vs. 27.6% in the conventional and intensive insulin therapy groups; P=0.9). Overall mortality rates at 6 months were similar in the 2 groups (18% vs.15%; P=0.9), as was the neurologic outcome at 6 months [modified Rankin score >3 in 22/38 patients (57.8%) in the conventional therapy group vs. 21/40 patients (52.5%) in the intensive insulin therapy group; P=0.7]. Intensive insulin therapy in patients with acute subarachnoid hemorrhage admitted to a postoperative neurosurgical ICU after surgical clipping of intracranial aneurysms decreases infection rates. The benefit of strict glycemic control on postoperative vasospasm, neurologic outcome, and mortality rates does not seem to be affected by intensive insulin therapy.