This article is from the Depression FAQ, by Cynthia Frazier with numerous contributions by others.
There is no scientific evidence that ECT causes brain damage. A woman who had over 1,000 ECT died of natural causes, and her brain was examined for evidence of ECT-induced brain damage. None was found. ECT does cause memory problems. These memory problems may take a number of months to clear. A small number of people who have received ECT complain of longer lasting memory problems. Such problems do not show up on psychological tests, it is not clear what causes them.