Incorrect alignment of the spinal column causes stress and unnecessary stress affecting the locomotor system. The objective of this study was to identify and establish the prevalence of hyperkyphosis and hyperlordosis and its relationship with body mass index (BMI) and waist-height ratio (WHR) in 12-year-old students from Arica, Chile. Eighty male students (n = 80) from three types of school: public, private subsidized, and private nonsubsidized schools were recruited. They were assessed weight (kg), height (m), BMI and WHR as an indicator of metabolic risk. The sagittal arrow test was used for postural evaluation of hyperkyphosis and hyperlordosis. Kruskal-Wallis tests, one-way ANOVA and Fisher's exact test and Chi-square test were used for the categorical variables. The results show a total prevalence of postural alteration of 57.5 %, a BMI of overweight / obesity of 52.5 % and a 35 % of metabolic risk. There was no association between BMI, WHR and spinal alterations, except for WHR and hyperkyphosis. The most frequent alterations were hyperlordosis followed by hyperkyphosis with 38.8 % and 25.7 % respectively, where the highest prevalences were recorded in the public school. In the sample studied we report the high prevalence of hyperkyphosis and hyperlordosis that there were not association with the indexes of overweight and obesity. In addition, the higher prevalences of postural alterations in the sagittal plane were reported in the public school. The prevention of postural alterations and the control of overweight and obesity should be carried out early in the whole elementary education system.