Purpose: The study investigates the predictive value of body image, self-esteem and gender for adolescent dieting at ages 15, 18 and 21 and whether adolescents' self-esteem moderates the relationship between body image and dieting. Method: Data stem from the Norwegian Longitudinal Health Behaviour Study (NLHB study): Adult by the Year 2000 ('Voksen i år 2000'). The NLHB study is a 10-year prospective cohort study based on self-completed questionnaires investigating health behaviour and lifestyle patterns among Norwegian adolescents. This paper presents data from Wave II (1992), Wave IV (1995) and Wave VI (1998), thus covering the ages 15, 18 and 21. Analyses are based on the 487 respondents participating at all three timepoints. Results: At all ages included, 25% of the girls reported they had dieted several times over the past year, while the corresponding figure for boys was 5%. Among boys, self-esteem and body image contributed to the same extent in the prediction of dieting, while only body image proved a significant predictor among girls, increasing in importance over time. Interaction between selfesteem and body image was present among young boys (ages 15 and 18) only. Conclusions: Self-esteem and body image play quite different roles in the prediction of dieting among girls and boys. The difference is not only related to strength of association between the variables, but, more importantly, to qualitatively different underlying processes.