Gonadotrophs in the anterior pituitary secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Neonatal diethylstilbestrol (neoDES) treatment affects reproductive function of male and female mice, but the effect of this treatment on the development as well as direct effects on pituitary gonadotrophs have not been ascertained. We investigated LH-secreting gonadotropes and the expression of genes involved in the synthesis and secretion of gonadotropins in the anterior pituitary of neoDES mice using immunohistochemistry and real-time reverse transcription-polymerase chain reaction (RT-PCR). The percentage of LH-secreting gonadotropes in 90-day-old female mice treated neonatally with an oil vehicle (neoOil) was significantly lower than in 30-day-old neoOil females but not in males, indicating a significant reduction after reproductive maturation in females. The percentage of LH-secreting gonadotropes in the medial area of 90-day-old neoDES females was significantly lower than that of 90-day-old neoOil females, ovariectomized neoOil females, and neoOil and neoDES males. The expression of the LH beta (Lhb) subunit in the anterior pituitary of 90-day-old neoDES females was similar to that in neoOil females, but it was significantly lower than that observed in 90-day-old males. Ovariectomy increased the expression of the alpha subunit of glycoprotein hormones, FSH beta (Fshb) subunit and Lhb subunit both in neoOil and neoDES females, suggesting that the anterior pituitary of neoDES female mice is regulated by ovarian hormones via negative feedback. In organ-cultured, anterior pituitaries exposed to DES exhibited no change in the number of LH-secreting gonadotropes but did reduced gene expression. These results suggest that LH-secreting gonadotropes in the female mice are not only directly affected by neoDES but also are influenced by the masculinization of the hypothalamus. That is, neonatal DES exposure can masculinize or defeminize the hypothalamus of female mice. However, the regulation of the pituitary gonadotropins by the hypothalamus could be different from that in intact male mice.