A retrospective review of the medical records of 258 postmenopausal patients using estradiol and testosterone implants as combined hormone therapy was carried out to evaluate the effects of testosterone on the endometrium after two years of continuous use. Endometrial thickness was measured by ultrasonography. Histology was performed on samples of thickened endometria obtained during hysteroscopy with biopsy. In the 44 patients in whom endometrial thickening was >5 mm at the end of the second year of implant use, the most frequent finding at hysteroscopy was polypoid lesion in 61.3% of cases, followed by normal uterine cavity in 31.8% of cases and submucous myoma in 6.8%. Histology of the endometrial samples confirmed endometrial polyp in 38.6% of cases, a histologically normal endometrium in 31.8% of cases, simple endometrial hyperplasia in 20.4% of cases, and myoma and atrophic endometrium in 4.5%. It is possible that testosterone may exert its antiproliferative effects on the endometrium but not on polyps in an action similar to that exerted by combined estrogen/progestin therapies. A greater incidence of simple, low-grade endometrial hyperplasia was found in our study compared with studies using continuous estrogen/progestin regimens. The use of progestins as the ideal endometrial protection should therefore be reconsidered.