✓ After intracranial surgery for an aneurysm, postoperative angiography should be routine. This may demonstrate lesions such as arterial spasm and hematoma, and may also show, sometimes quite unexpectedly, that the sac has not been completely obliterated. A clip or ligature may be merely misplaced, not be closed tightly enough, slip, or include the parent artery. In our series of 329 patients who underwent postoperative angiography, contrast filling of a significant part of the sac still occurred in 43 (13%); at least 12 of these rebled. Further intracranial surgery was carried out in 18, with satisfactory obliteration of the sac in 16. An incompletely obliterated aneurysm should be reoperated on as soon as possible. The risk involved at this time is minimal and far less than the possibility of another catastrophic hemorrhage.