Using data gathered through questionnaires on factors relating to the intention of condom use included in the Theory of Planned Behavior, we obtained evidence in favor of the two-dimensional structure of attitude: affective and cognitive components. In a structural equation model for predicting the intention of condom use as an instrumental behavior, we found that the congruence between the affective and cognitive components moderates the influence of attitude, subjective norm and perceived behavioral control in the intention of condom use. Since most of the studies do not take into account this proposed interaction, they can only report a kind of main effects average. Moreover, the percentage of explained variance of intention is higher for those individuals with the same value for the two components (congruent group). Furthermore, we found that perceived behavioral control is the most determining factor and that the cognitive component of the attitude is a better predictor than the affective one. The results are discussed from the point of view of their implications for designing prevention programmes for sexually transmitted diseases.