Purpose. The objective of this study was to evaluate the prevalence of body shape concerns and associated factors among Brazilian early adolescents. Methods. This was a school-based cross-sectional epidemiological study conducted with 526 girls between 11 and 14 years enrolled in thirteen public schools in Florianópolis, Santa Catarina, Brazil. The Body Shape Questionnaire and Eating Attitude Test (EAT-26) was administered. Sociodemographic variables (age group, household head education, and socioeconomic status), sexual maturation (pubic hair growth, breast development, and menarche) and percentage of body fat (%BF) were collected. Analyses were conducted using Poisson regression and a confidence level of 95%. Results. The prevalence of body shape concerns was 24.1% (95% confidence interval - CI: 17.5-30.7). Adolescent girls aged 13-14 years (prevalence ratio - PR = 1.07, 95% CI: 1.03-1.11; p = 0.02), with very high (PR = 1.52, 95% CI: 1.21-1.90; p = 0.004) and high %BF (PR = 1.25, 95% CI: 1.18-1.32; p = 0.004), and those girls showing risk behaviors for anorexia and bulimia (PR = 1.37, 95% CI: 1.19-1.59; p = 0.01) were more concerned with their body image. Conclusions. The prevalence of body shape concerns among Brazilian girls was considerable and was associated with age, %BF, and risk behaviors for anorexia and bulimia. This study highlights the importance of screening for body image concerns in schools, preventing the adoption of unhealthy body weight ideals, and the development of excessive body shape concerns in this population.