I) Endocrinological changes in girls during puberty are characterized by the progressive elevation of pituitary, ovarian and adrenal hormones except PRL. Longitudinal study revealed significant increases in both LH, FSH and estradiol occurred between 2 years to one year before menarche. PRL levels, however, increased between 3 to 2 years before menarche and the levels dropped significantly one year before the onset of the first menses. Serum levels of androstenedione and estrone in girls were higher than that in boys. Among steroids, the levels of 5 alpha-androstanediol decreased significantly before the menarche suggesting the physiological role of this hormone on the onset of puberty. In regard to the correlation between hormone levels and sexual developments, DHA-S levels and body weights correlated well with the breast development. Grasping power correlated well with serum testosterone levels in girls. II) The clinical and endocrinological aspect of menstrual disorders during adolescent were also examined. The majority of the patients complaining of functional uterine bleeding and amenorrhea showed high LH and normal FSH levels. Episodic secretion of LH was absent in girls of primary and secondary amenorrhea due to hypothalamic impairment.