Objective: The objective of this study was to detect any ovarian changes in ta moxifen-treated breast cancer patients. Methods: In all, 51 patients with breas t cancer were enrolled in the study, which was conducted in the SSK (Social Secu rity Agency) Aegean Maternity Hospital between January 1999 and December 2002. T he patients’demographic and medical data were reviewed. All patients taking par t in the study received tamoxifen therapy, but the duration was not uniform. Gyn ecological examination and transvaginal ultrasonography (TVU) were performed in each case. Any ovarian cysts or masses were identified, and serum Ca-125 levels were recorded. Results: Of the 51 tamoxifen-treated patients enrolled in this study, 24 were still premenopausal and 27 were postmenopausal when they were mon itored for breast cysts during the tamoxifen treatment started after the diagnos is of breast cancer. Their average age was 53.7 (range 31-64) years. The mean d uration of tamoxifen therapy was 23.5 (range 8-49) months. Ovarian cysts were d iagnosed in nine (17.6%) patients and required surgery in two of these; patholo gical examination revealed serous cysts of the ovary in both. Conclusion: In cas es with ovarian cyst formation during tamoxifen treatment of breast cancer, disc ontinuation of tamoxifen followed by monitoring is quite a reasonable way to pro ceed in most cases. Surgical intervention should be carried out when cysts are > 5 cm in diameter. Objective: The objective of this study was to detect any ovarian changes in ta moxifen-treated breast cancer patients. Methods: In all, 51 patients with breas t cancer were enrolled in the study, which was conducted in the SSK (Social Security Agency ) Aegean Maternity Hospital between January 1999 and December 2002. All patients taking par t in the study received tamoxifen therapy, but the duration was not uniform. Gyn ecological examination and transvaginal ultrasonography (TVU) All ovarian cysts or masses were identified, and serum Ca-125 levels were recorded. Results: Of the 51 tamoxifen-treated patients enrolled in this study, 24 were still premenopausal and 27 were postmenopausal when they were monitored for breast cysts during the tamoxifen treatment started after the diagnos is breast cancer. Their average age was 53.7 (range 31-64) years. The mean d uration of tamoxifen therapy was 23.5 (range 8-49) months. Ovarian cysts were d iagnosed in nine (17.6%) patients and required surgery in two of these; patholo gical examination revealed serous cysts of the ovary in both. Conclusion: In cas es with ovarian cyst formation during tamoxifen treatment of breast cancer, disc ontinuation of tamoxifen followed by monitoring is quite a reasonable way to pro ceed in most cases. Surgical intervention should be carried out when cysts are> 5 cm in diameter.