Background: Body dissatisfaction (BD)—a health concern in its own right—often is positioned early in the causal chain toward eating pathology, and is a practical point of intervention for those aiming to reduce its negative health consequences. One approach to reducing people’s resistance to receipt of other unwanted health information (e.g. about smoking) has been through the application of self-affirmation theory. This theory asserts that the self needs to maintain its integrity and, as such, when incoming information is threatening, one’s defensive shields are activated and it is deflected. One way to reduce defensiveness, however, is to bolster some other aspect of the self. Method: We applied a one-shot, self-affirmation-based manipulation via a randomised controlled design (N = 86) to a group of body-dissatisfied college women and compared its effects to a control group. Results: All hypotheses predicted by self-affirmation theory were supported: Women who were self-affirmed exhibited (a) greater openness to threatening information about the dangers of BD, (b) lower BD, and (c) greater intention to reduce criticism of their bodies. Conclusions: The present study provided an experimental test of a mechanism of action which might prove useful in a comprehensive intervention program.