Context: Detailed evaluation of pubertal progression in girls from longitudinal studies is sparse, and the phenomenon of transient thelarche (TT), defined as the appearance, regression, and subsequent reappearance of breast buds, in healthy girls remains undescribed.

Objective: To describe TT in terms of pubertal progression, growth, genotypes, and reproductive hormones and to apply new puberty nomograms for breast stages, pubic hair, and menarche.

Design: A prospective, longitudinal population-based study.

Patients or Other Participants: Ninety-eight healthy Danish schoolchildren (Caucasian girls) followed longitudinally as part of the COPENHAGEN Puberty Study were included in the evaluation of TT. A total of 1466 girls from 2 cross-sectional studies were included in the creation of the puberty nomograms.

Intervention(s): None.

Main Outcome Measure(s): Pubertal progression, specifically thelarche, reproductive hormones, genotype, and growth.

Results: Twelve of 98 (12%) girls experienced TT. A larger proportion of girls with TT entered puberty by the pubarche pathway (50%) compared with girls with normal progression (15.4%), P = 0.014. Girls with TT progressed through puberty normally when evaluated using puberty nomograms. Reproductive hormones and growth velocity were lower at the first (transient) thelarche than the second (permanent) thelarche.

Conclusion: TT is a frequent phenomenon that appears to be a peripheral occurrence independent of central puberty. It does not appear to affect subsequent pubertal progression as evaluated by our new puberty nomograms.