Laboratory studies of voluntary memories have been criticized for being too insensitive in detecting the impact of trauma. To overcome this, 12 traumatized undergraduates participated in a diary study of involuntary memories (8 females, 4 males, mean age 25 years, range 19–33). Six participants had encountered their trauma more than five years ago, six within the most recent year. No group differences were found on frequency and vividness of involuntary trauma memories, their mood-impact and ability to trigger a physical reaction. Marked differences were found between traumatic and non-traumatic involuntary memories on the same variables. The results indicate that trauma memories are extraordinarily persistent. This was confirmed by a comparative study of memory for extremely happy events (9 females, 5 males, 26 years, range 20–38). Further, it was demonstrated that highly vivid involuntary memories—so-called flashbacks—are not limited to trauma nor even to emotionally negative events. Copyright © 2001 John Wiley & Sons, Ltd.