Tamoxifen is the primary hormonal therapy for breast cancer as well as its chemoprevention. It is used in the management of breast cancer because of its anti oestrogenic effect. It is however an agonist on the endometrium with undesirable effects of endometrial proliferation with the risk of endometrial hyperplasia and carcinoma. Several authors have reported cases of endometrial hyperplasia and carcinoma following tamoxifen therapy for breast carcinoma. No such report has been made from Nigeria . This paper presents the first case of endometrial carcinoma following tamoxifen therapy for breast carcinoma in a 52 year old Nigerian female. It also highlights the recommended guidelines for the follow up of women with breast cancer on tamoxifen therapy.