We investigated how smiles influence perceptions of what the eyes are expressing, whether happy or sad, compared to the influence of sad or angry mouths. Participants were thirty-six first year Psychology students. Participants initially looked at the mouth and then judged whether the eye expression was happy, sad or angry or not. The expression of the eyes and mouth could be congruent (eg, both happy) or incongruent (eg, fearful eyes, smiling mouth); the eyes were visible but the mouth was masked in the control condition. The results suggest that, under eye-mouth congruence conditions, looking at the smiling, sad and angry mouths similarly facilitated the correct identification of the eyes. In contrast, under incongruence conditions, a smiling mouth led to greater interference than sad or angry mouths; that is, the smile misled the viewers into judging non-happy eyes as happy, and increased the time needed to correctly identify their expression. The facilitation effects are explained by a priming mechanism guided by the first gaze directed at the mouth. The interference effects are explained as a function of the high visual saliency and diagnostic value of the smile.