Premature estrogenic effects may result from exogenous exposure to estrogenic substances. We report the case of a 36-month-old girl who presented with vaginal bleeding, uterus enlargement, and thelarche. Questioning of the parents revealed that the child's mother had used hormone-based hair lotions on her own scalp and that the child was in the habit of playing with her mother's hair while falling asleep, and that the girl played with her mother's combs and the empty lotion vials. The onset of hyperestrogenic syndrome was temporally related to the handling of lotions containing ethynylestradiol 0.5%. Analysis of long scalp hairs from the girl and her mother identified ethynylestradiol in concentrations of 10.6 and 46.6 microg/g, respectively. Six months after the mother discontinued use of the estrogen-containing hair lotion, the girl's hyperestrogenic signs resolved. This case highlights the importance of obtaining histories of possible food and non-food environmental sources of contamination, the suitability of hair sampling to identify the origin of the contamination, and the opportunity to warn parents about hazards related not only to oral contraceptives, but also custom-compounded topical hormone preparations.