The effect of a 1-year exercise and diet intervention program on global self-concept, perceptions of the body, physical competence, exercise mastery, social competence, social comfort, and fitness was examined with 208 healthy individuals (191 males, 17 females) aged 39-49 years (mean age 44.9) with elevated risk factors for cardiovascular disease. The relative utility of the skill development versus the self-enhancement model of the self-concept/behaviour relationship was tested. The participants were randomized into four groups: diet (n = 53), diet and exercise (n = 64), exercise (n = 48) and no active intervention (n = 43). Measurements were made by the Harter adult self perception profile (HASPP) and the self-perception in exercise questionnaire (SPEQ). Two-way ANOVA analyses revealed that exercise participation, with or without diet, enhanced self-perceptions of physical mastery and ability, body perception, fitness and social comfort. The unique contribution of diet indicated enhanced body perception. No effect was found of diet or exercise on global self-concept. Exercise participation had a positive effect on perceptions of the self, and the higher the compliance with the exercise program, the stronger were the effects on the self-perceptions. This supported the skill development model of the self-concept/behaviour relationship. As the pretest self-concept scores did not predict exercise compliance, the self-enhancement model of the self-concept/behaviour relationship was not supported.