Health messages framed to be congruent with individuals' approach/avoidance motivations have been found to be more effective in promoting health behaviors than health messages incongruent with approach/avoidance motivations. This study examines the processes underlying this congruency effect. Participants (undergraduate students, N = 67) completed a measure of approach/avoidance orientation (the BIS/BAS scales) and read either a gain- or loss-framed message promoting dental flossing. Results demonstrated a congruency effect: Participants who read a congruently framed message had greater flossing efficacy, intended to floss more, and used more dental flosses than did the participants who read an incongruent message. Moreover, intention to perform the behavior predicted the congruency effect and self-efficacy mediated participants' intentions to perform the health behavior. Discussion centers on the role of personality factors and situational factors in models of behavior change.