Endometrial thickness greater than 4 to 5 mm on ultrasound is considered abnormal in postmenopausal women. A small number of women with endometrium thicker than 5 mm by ultrasound will have atypical hyperplasia or carcinoma (Langer). Women who take tamoxifen often have abnormally thickened endometrium on ultrasound. Use of tamoxifen increases a woman's risk of endometrial cancer. However, what appears to be endometrial thickening on ultrasound in women taking tamoxifen might actually be stromal edema and not endometrial hyperplasia (Bornstein). Endometrial thickening may signal hyperplasia or malignancy and may be an indication for biopsy. Whether every asymptomatic woman who takes tamoxifen needs serial screening transvaginal ultrasound or endometrial biopsy is controversial.