This preliminary study applied Self-Categorization Theory (SCT) to the sexual bullying of high school girls by boys. Seventy-five Year 9 boys responded to vignettes portraying sexual bullying in which gender was a more or a less salient feature of the social context described. As predicted, boys were more likely to engage in sexual bullying when gender was more salient. Masculine sex role was not correlated with engagement in sexual bullying. Controlling for social desirability, pro-bullying attitude was predictive of such engagement, but only when the social context rendered gender less salient. This suggests the power of the perceived social context for determining which individual characteristics will gain expression. It is concluded that SCT is a promising avenue for advancing understanding of bullying, a field of research that has previously largely lacked a theoretical focus.