The relationship between defensive style and concept formation with aggressive and neutral stimuli was investigated. Very strong relationships were found between the use of avoidant and repressive defenses and the number of errors made in acquiring and utilizing an aggressive concept. This relationship was not found for the neutral concept. The results suggest the importance of directing attention to the relevant stimulus dimension in efficient concept formation. Insofar as defensive style involves a particular way of deploying attention (e.g. avoidance of a particular content) and insofar as the affective nature of the stimulus material lends itself to the elicitation of defensive reactions, individual differences in defensive style can serve as a robust predictor of efficiency of concept formation.