Objective. To estimate the prevalence of lateral and anteroposterior postural changes in female adolescents and to investigate whether these changes are associated with certain socioeconomic, demographic, anthropometric, or behavioral variables. Methods. This epidemiologic survey included a representative sample of 495 high school students from regular day school programs in the city of Sao Leopoldo, Rio Grande do Sul, Brazil, which is in the South region of Brazil. The students, who were 14 to 18 years old, were assessed in October and November of 2004. Postural changes were defined as skews in the spinal curvature, identified through noninvasive postural assessment. Results. The prevalence of lateral changes was 66% (95% confidence interval (CI): 61.5% to 70.0%) vs. 70% for anteroposterior changes (95% CI: 65.2% to 73.5%). Lateral changes were more prevalent in students with a normal body mass index ( prevalence ratio (PR) = 1.32; 95% CI: 1.09 to 1.59) and in those who watched television for more than 10 hours weekly (PR = 1.16; 95% CI: 1.02 to 1.32). The prevalence of anteroposterior changes was higher in students whose parents/guardians had no schooling or only had elementary schooling (female guardians: PR = 1.30, 95% CI of 1.09 to 1.55; male guardians: PR = 1.20, 95% CI of 1.02 to 1.40) and in students who were overweight or obese (PR = 1.33; 95% CI of 1.19 to 1.48). Conclusions. The high prevalence of postural changes observed is reason for concern since these changes can translate into spinal problems in the medium to long term. Health professionals, including physical education teachers, should be trained to perform postural assessments, which should be routinely done in schools.