Attitudinal ambivalence is generally construed as existing when the same attitude object is evaluated simultaneously as both positive and negative. The present research examined the moderating role of attitudinal ambivalence (as assessed by split-semantic differential measure) on the relationship between bipolar semantic differential measures of attitude and subsequent behaviour using moderated regression analysis. In Study 1, higher levels of attitudinal ambivalence were shown to result in weaker attitude–behaviour relationships for eating a low-fat diet (N = 140) and eating 5 portions of fruit and vegetables per day (N = 142). Study 2 (N = 361) replicated this effect when also including a measure of past behaviour for eating a low-fat diet. Implications for understanding the relationship between attitudes and behaviour are discussed. Copyright © 2002 John Wiley & Sons, Ltd.