Aromatase inhibitors (AIs) are important adjunctive therapy for postmenopausal women with hormone receptor-positive, early-stage breast cancer. At the present time, AIs have no role for the management of breast cancer in premenopausal women. We report on several cases of the inadvertent use of AI therapy among women with residual ovarian function. A common experience in these cases was the onset of chemotherapy-related amenorrhea before initiation of AI therapy, which confounded assessment of true menopausal status. We believe clinicians should be aware of the potential ovarian reserve among women with treatment-related amenorrhea so as to avoid use of AI therapy in patients in whom there is uncertainty about menopausal status.