Endovascular treatment for acute ischemic stroke has the potential to substantially improve the outcome for select individual stroke patients. However, the impact of this treatment on a population scale is unknown. We reviewed the epidemiology of acute stroke presentation times to estimate the proportion of patients with ischemic stroke who may be eligible for intra-arterial treatment. Experience with IV thrombolysis suggests that time from symptom onset is likely to be among the major exclusion criteria for intra-arterial treatment. Studies reviewed suggest that between 5% and 13% of patients with ischemic stroke present in the commonly recommended intra-arterial treatment window of 3 to 6 hours. Because of clinical exclusion factors other than time, the proportion of stroke patients eligible for intra-arterial treatment is likely even lower than these estimates. Clinicians and researchers should consider this a modest proportion of eligible patients when planning future studies and creating referral networks for endovascular stroke treatment.