Objectives External skeletal robustness has been decreasing in children, potentially due to a lack of physical activity and the increased prevalence of obesity. However, whether socioeconomic status (SES) influences external skeletal robustness in adolescents has not yet been examined. Methods A cross-sectional study was performed to examine 370 Chilean adolescents (16.15 +/- 1.01 years old) recruited from distinct educational establishments. Body fat percentage (BF%) was evaluated using Ellis' equations for Hispanic children. Obesity was defined as >= 25 BF% in males and >= 30 BF% in females. External skeletal robustness was obtained by measuring the humerus biepicondylar width and height (Frame-Index). SES was obtained through the ESOMAR survey. Results Females exhibited significantly greater BF% and lower Frame-Index values than males (P < .001). Obese adolescents (by BF%) had greater Frame-Index values than non-obese adolescents (P < .001). Females of medium-high SES had significantly lower BF% and Frame-Index values than females of medium and medium-low SES. BF% had a positive correlation with Frame-Index values in all SES groups studied, except in males of medium-high SES. As SES decreased, the correlation increased in both sexes, but overall, the correlation was greater in females than males. Conclusions The results of this investigation suggest that obesity increases external skeletal robustness in adolescents. Additionally, lower SES corresponded to higher BF% and Frame-Index values. Therefore, modern conditions that influence the prevalence of obesity in adolescence could be affecting bone health in adolescents, primarily in females of medium-low SES.