Persistent cerebral blood flow occasionally confounds confirmatory tests for brain death and results in the anguish of delayed diagnosis, unnecessary use of expensive resources, and loss of transplant opportunities. We reviewed the literature to examine the reasons, frequency, and meaning of this problem. We found that this phenomenon occurs: (1) before increasing intracranial pressure completely shuts down flow; (2) in infants with pliable skulls; and with (3) decompressing fractures, (4) ventricular shunts, (5) ineffective deep brain flow, (6) reperfusion, (7) brain herniation, (8) jugular reflux, (9) emissary veins, and (10) pressure injection artifacts. Isolated venous sinus visualization is common (occurring in up to 57%) but represents trivial blood flow and confirms brain death. Arterial flow is much less common (2.6% incidence in our series). Normal flow occurs but is rare. Arterial flow does not exclude brain death, but the diagnosis should be confirmed by repeated studies or other means.