Despite the number of reported data concerning idiopathic central precocious puberty (CPP) in girls, major questions remain including its diagnosis, factors, and indications of gonadotropin releasing hormone (GnRH) analog treatment. A retrospective, single-center study was carried out on 493 girls with CPP. Eleven girls (2.2%) were aged less than 3 years. Breast development was either isolated (Group 0, n = 99), or associated with one sign, pubic hair development, growth rate greater than 2 standard deviation score (SDS) or bone age (BA) >2 years above chronological age, (Group 1, n = 187), two signs (Group 2, n = 142) or three signs (Group 3, n = 65). The interval between onset of puberty and evaluation, body mass index (BMI) SDS, plasma luteinising hormone (LH) concentrations (basal and peak) and LH/ follicle-stimulating hormone (FSH) peak ratio after GnRH test, plasma estradiol and uterus length were significantly greater in Groups 2 and 3 than in Groups 0 and 1 respectively. 211 (42.8%) patients were obese and/or had excessive weight gain during the year before puberty. Obese girls more often had BA advance of >2 years (p = 0.0004) and pubic hair development (p = 0.003) than the others. BMI did not correlate with LH or with LH/FSH peak ratio. Girls with familial history of early puberty (41.4%) had greater frequencies of pubertal LH/FSH peak ratios (p = 0.02) than the others. During the 31 years of the study, there was no increase in the frequency of CPP or variation in its characteristics. Obesity is associated with a higher BA advance and higher frequency of pubic or axillary hair development but not with LH secretion, suggesting that obesity accelerates adrenarche but not the maturation of the hypothalamic-pituitary-ovarian axis. The LH/FSH peak ratio was more frequently pubertal in girls with a familial history of early puberty, suggesting that this maturation depends on genetic factors.