Changes in body mass index (BMI) among girls with idiopathic central precocious puberty (ICPP) under treatment have been controversial in other populations. To assess changes in BMI Z score and the rate of overweight and obesity in Mexican girls with ICPP during their first year of treatment. A retrospective study was conducted among girls with ICPP under treatment with leuprolide, with a somatometry performed every six months, over a 1-year period. An analysis of variance (ANOVA) was done to establish differences in BMI Z score and a multivariate analysis was used to assess the relationship among the different factors. Among 121 girls, BMI Z score increased from 0.87 to 1.32, and the rate of overweight and obesity increased from 40.5% to 70.3%, a statistically significant difference. Changes in BMI Z score and the rate of overweight and obesity among Mexican girls with ICPP increased significantly. Sociedad Argentina de Pediatría.