To evaluate whether body dissatisfaction is associated with disordered eating symptoms in Finnish preadolescents, and to assess the moderator effects of gender and body mass index on this association. We included 10,526 9- to 12-year-old preadolescents at baseline from the Finnish Health in Teens cohort. We used the Children's Eating Attitudes Test for assessing disordered eating symptoms and a pictoral instrument for evaluating body dissatisfaction, comparing self-assessment of wanted and current body shape. Odds ratio (OR) for disordered eating symptoms were estimated using unconditional logistic regression. A high percentage of preadolescents reported body dissatisfaction: 30.0% wanted a smaller body and 9.3% wanted a larger body. Only 2.2% of the participants had disordered eating symptoms. Preadolescents who wanted a larger (OR = 2.83; 95% confidence intervals (CI): 1.68-4.78) or smaller body (OR = 4.48; 95% CI: 3.20-6.26) had a higher risk of having disordered eating symptoms, compared to preadolescents satisfied with their body. Among preadolescents who wanted a smaller body, the effect of body dissatisfaction was more pronounced among girls (OR = 5.00; 95% CI: 3.25-7.70) than boys, and among normal-weight (OR = 6.82; 95% CI: 4.53-10.25) and underweight (OR = 23.23; 95% CI: 5.31-101.61) than overweight preadolescents. Body dissatisfaction is associated with disordered eating symptoms especially among girls, and those who are underweight and normal-weight. Our study suggests that, in the prevention of eating disorders, special attention should be given to preadolescents with body dissatisfaction.