Construct validity established for the Impact of Event Scale does not include evidence that the scale can distinguish genuine responses from simulated ones, an important requirement for cognitively “transparent” measures subject to systematic distortion by demand characteristics of the test situation. Comparison scores from 35 students coping with recent parental death and 30 randomly selected students instructed to respond as though they recently had a parent die indicated that, as predicted for this measure, simulated responses involved uniformly high endorsement of all items, while genuine responses were lower in magnitude and varied more from item to item. The scale appears to be adequately sensitive to differences between genuine and simulated responses.