AIM: Young people are often seen as an important target for prevention of overweight, but we know little about the factors which are important for their weight management decisions. This study aimed to evaluate the extent to which elements of body composition and dimensions were implicated in their decisions to change their weight. PARTICIPANTS: Participants were 116 male and 126 female volunteers from a tertiary college in the south-west of England with a mean age of 17.90 (s.d. 1.90) y. MEASURES: Body composition measures included height (m), weight (kg), waist and hip circumferences (mm), shoulder and hip girths (mm) and skinfold thicknesses (triceps, calf and subscapular, mm). Students also provided self-reported information on dietary practices they had undertaken in the last year. RESULTS: More females reported attempting weight loss in the last year compared to males (51.5 vs 17.6%), although more males reported attempting weight gain (19.3 vs 2.3%). Reported dietary strategies for both males and females centred around eating less fatty foods, eating less than usual and exercising more. However, a signi®cant proportion of females also reported excessive strategies, such as self-induced vomiting and regular crash dieting. Results indicated that females who desired to lose weight were signi®cantly (P`0.05) heavier, and bigger in terms of circumferences and skeletal breadths, compared to females who did not wish to change their weight. For males, thè weight loss' group were signi®cantly (P`0.05) bigger, heavier and fatter compared to the`no change and`weight gain' group. For females only, the previously signi®cant main effect for body dimensions across weight management groups (Pillais F 14,188 3.81, P`0.001) was extinguished when controlling for bone dimensions (Pillais F 12,198 1.68, P 0.074). CONCLUSION: These results indicate that frame size, particularly in the lower trunk, is a more important predictor of female weight management decision-making, than their levels of fatness. For males, fatness appears to drive their weight management decision-making processes to a greater extent.