Vestibular schwannomas have been noted to have increased frequency and aggressivity in female patients, suggesting a possible role of estrogen. This study evaluated the effects of estrogen and tamoxifen on the growth of human vestibular schwannoma tissue implanted in subcutaneous pockets of nude mice. Animals were implanted with 1 of 3 human vestibular schwannomas and observed for 28 days. Mice were then separated into 3 treatment groups: controls, estrogen (receiving 1.7 mg of 17B-estradiol), and estrogen + tamoxifen (receiving 1.7 mg of 17B-estradiol + 10 mg of tamoxifen), and treated for 28 days. Mice treated with estrogen showed increased growth that was statistically significant (P < 0.05) when compared with that of both the controls and the animals treated with estrogen + tamoxifen. Controls and animals treated with estrogen + tamoxifen showed a general trend of decreased volume during the treatment period. These early results support the hypothesis that estrogen modulates the growth of vestibular schwannomas in the nude mouse model and that these effects can be blocked by tamoxifen administration.