Head impacts in animal and human cadaver tests and in aircraft accidents are simulated using finite element brain models. Brain injury severity is correlated with peak intracranial pressure. The results show that serious and fatal injuries occur when the pressures exceed 34 psi. Considering this value to be the pressure tolerance limit of the brain, a brain injury criterion is proposed. Tolerance curves of head acceleration versus time for frontal and occipital impacts are presented. These the brain pressure tolerance curves are compared to existing head injury criteria (the Wayne State tolerance curve, the Vienna Institute model tolerance, the maximum strain criterion from the University of Michigan, the helmet standard, and the head injury criterion used by the Department of Transportation).