Levetiracetam is used for seizure prophylaxis in patients presenting with subarachnoid hemorrhage (SAH) or traumatic brain injury (TBI). We aim to characterize the optimal levetiracetam dosage for seizure prophylaxis. This retrospective cohort study included adult patients at an academic tertiary hospital presenting with SAH or TBI who received levetiracetam at a total daily dose (TDD) equivalent to or greater than 1000 mg. The primary outcome was combined seizure incidence, including clinical and subclinical seizures. We identified 139 patients (49.6% male, mean age 53 years) for inclusion. For patients receiving a 1000-mg TDD, the administration was 500 mg twice daily. For patients receiving >1000-mg TDD, 77/78 patients received 1000 mg twice daily and one patient received 750 mg twice daily. Patients receiving 1000-mg TDD had a higher seizure incidence than those receiving >1000-mg TDD (p = 0.01), despite no difference in examined confounders, including history of alcoholism (p = 0.49), benzodiazepine use (p = 0.28), or propofol use (p = 0.17). No difference in adverse effects was observed (anemia, p = 0.44; leukopenia, p = 0.60; thrombocytopenia, p = 0.86). Patients may experience a reduced incidence of clinical and electroencephalographic seizures with levetiracetam dosing >1000-mg TDD.