Females with Breast Development before Three Years of Age.

Breast development in a girl 3 years of age or younger is a commonly encountered scenario. Nearly all of these cases will either regress or fail to progress during follow-up, confirming a diagnosis of premature thelarche (PT). Studies show that these girls will have onset of true puberty and menses at a normal age. The authors present evidence that laboratory testing, particularly basal and gonadotropin hormone-releasing hormone -stimulated gonadotropin levels, will show overlap between girls with PT and the rare patients with the onset of central precocious puberty before age 3, mainly of whom have hypothalamic hamartomas.