Abstract: Objective To observe the clinical course of isolated premature thelarche (IPT) in female infants under two years of age.Methods A total of 74 female infants with IPT, who visited the Department of Endocrinology in Beijing Children's Hospital from Feb. 2011 to Dec. 2011, were followed up for 5 years. Results Twelve cases were lost to follow-up, 83.78% (62/74) cases completed the 5 years follow-up. For total 74 cases, the median age was 63.50 months (38.86, 70.33), the median duration of follow-up was 54.9 months (21.75, 56.33). The median age of premature thelarche was 9.02 months (5.67, 14.07). Within the duration of 25 months, the velocity of relief was faster. At the end of the last visit, 96.77% (60/62) premature thelarche was relieved to Tanner I, the median relief age was 30.72 months (24.54, 35.89); According to the age of onset, all cases were divided into two groups: classical and non-classical IPT, compared with their relief rate of premature thelarche, there was no significant difference. During 5 years follow-up, 2 cases had persistent thelarche and there was no evidence of developing into central precocious puberty. Conclusion Most isolated premature thelarche have a benign prognosis among female infants under 2 years old. A longitudinal follow-up study is necessary for isolated premature thelarche cases.

Key words: female, infant, isolated premature thelarche, prognosis