Reported changes in body mass index (BMI) in central precocious puberty (CPP) during and after gonadotropin-releasing hormone analog (GnRHa) treatment are inconsistent. We, therefore, investigated weight gain and auxological parameters in GnRHa-treated girls with idiopathic CPP (ICPP) until attainment of near final height (NFH). From the medical records of 59 ICPP girls who attained NFH after GnRHa therapy, auxological changes in height, weight, BMI, and predicted adult height ( PAH) were compared between overweight (BMI ≥ 85 percentile) and normal-weight (BMI 85 percentile) groups. BMIs were changed into standard deviation scores (BMISDSs) for subject’s chronologic age (BMISDS-CA) and bone age (BMISDS-BA). The incidence of overweight including obesity in the study population was high at the start of therapy (35.6%). In both groups, the height increased significantly during and after cessation of therapy, and PAH at the start of therapy was significantly shorter than the mid-parental height (MPH), whereas PAH at end of therapy approached MPH, and NFH was greater than MPH. All subjects’ BMI significantly increased during and after therapy at NFH. Both BMISDS-CA and BMISDS-BA increased significantly during therapy, but, after therapy both BMISDSs decreased significantly until NFH. At NFH both BMISDSs were not different from those at baseline. In the normal-weight group, both BMISDSs increased during therapy and maintained that level until NFH. In overweight group, neither BMISDS changed during therapy, but there was a decrease after therapy until NFH. Auxological parameters were not different between the two groups. The BMISDSs increased during GnRHa therapy, then decreased to the pretreatment level at NFH. However, patterns of BMISDS change were different between the normal-weight and overweight groups.