For almost 45 years, the experience of Jewish children who were hidden during World War II was considered to be of little importance, particularly with respect to what had taken place in the concentration camps. Their very history was ignored in the many accounts of the Holocaust. It was only at the end of the 1980s that their experience began to be thought of as potentially traumatic. In this paper, the authors report on their psychoanalytical research project concerning the psychological outcomes of those experiences that had remained concealed for such an extraordinarily long latency period. The results are based on the analysis of 60 accounts and on psychoanalytically-oriented group work. The authors show that the trauma experienced by those hidden children was triggered by the retroactive effect of a deferred action [après-coup].