Antifibrinolytic treatment for 4 weeks after a subarachnoid hemorrhage has been shown to have no effect on outcome since a reduction in the rate of rebleeding was offset by an increase in ischemic events. To determine if a shorter course (4 days) of antifibrinolytic treatment before the expected onset of ischemic complications might reduce the rate of rebleeding yet avoid ischemic complications, we prospectively studied a series of 119 patients with subarachnoid hemorrhage; 479 patients with subarachnoid hemorrhage from our previous randomized double-blind study (238 treated with placebo, 241 with long-term tranexamic acid) served as historical control groups. At 3 months' follow-up, the outcome of patients treated with short-term tranexamic acid was not different from that of patients treated with long-term tranexamic acid. The rate of rebleeding (24 of 119, 20%) was near that with placebo (56 of 238, 24%). In contrast, the rate of cerebral infarction (33 of 119, 28%) was almost identical to that after long-term tranexamic acid (59 of 241, 24%), although mortality from cerebral infarction was reduced. Compared with historical control groups, treatment with tranexamic acid for 4 days fails to reduce the incidence of rebleeding but still increases the rate of cerebral infarction.