Breast cancer is the most common malignancy encountered in reproductive age women, and the majority of chemotherapy regimens contain the gonadotoxic alkylating agent cyclophosphamide with adriamycine (AC), and recently taxanes (ACT). While the negative impact of alkylating agents on fertility has been recognized, much less is known about the effects of newer adjuvant regimens such as taxanes (T) on ovarian function. Our goal was to determine whether addition of taxanes impacted ovarian function as assessed by both menstrual history and ovarian reserve markers. Prospective observational study with ovarian reserve assessment. Forty-five women with breast cancer stage I-IIIA who had received either AC+T (n=28) or AC (n=17) were enrolled in the study. Patients were asked to keep a record of their menstruation during and after chemotherapy treatment, and the incidence of amenorrhea was analyzed six months after the completion of chemotherapy. A second follow up was done after a mean 28.2 months (range 15-86 months) post chemotherapy when patients were interviewed regarding menstruation and menopausal symptoms. At that follow up, patients were also asked to undergo a random day 2 or 3 (if menstruating) serum hormonal measurement for follicle stimulating hormone (FSH), estradiol (E2), and luteinizing hormone (LH) at our institution. Patients having received ACT were younger than those having receiving AC (34.0 ± 1.0 vs. 37.2 ± 1.0) (p<0.05). A higher percentage of patients receiving ACT experienced persistent amenorrhea 6 months after chemotherapy (14/28; 50%) compared to AC (5/17, 29%)(p=0.03), despite their younger age. Of the 45 patients that were reached in the first follow up, twenty patients were excluded at the second follow up because of receiving additional chemotherapy (n=3), undergoing oophorectomy (n=1), developing a new primary cancer (n=1), refusal (4), or inability to contact (11). Twenty-five patients were included in the second follow up, of which 14 received ACT and 11 received AC. In contrast to the short-term findings, the difference between the incidence of amenorrhea or menopausal symptoms in ACT patients (35.7% and 50.0%) versus AC (9.1% and 27.3%) at our second follow-up did not reach statistical significance. In fourteen patients (ACT n=9; AC n=5), we were able obtain day 2 or 3 serum FSH and E2 measurements. Of the eleven menstruating women with an average age of 39.6 (+/- 3.8 years), abnormally elevated FSH (DPC >12.0 mIU/ml) or E2 levels (DPC>85 mIU/ml) were found in 3/6 ACT and 5/5 AC patients. Thus, when including the hormonal assays as a marker of ovarian reserve, an additional eight patients were identified, bringing the incidence of compromised ovarian function to 57.1% (8/14) and 54.5% (6/11) after ACT and AC respectively. Although the short-term incidence of amenorrhea is higher in patients who were treated with taxanes, we found no significant long-term impact of taxanes on ovarian function, particularly when day 2-3 FSH and estradiol evaluation was included. Because we have identified 11 patients of whom 8 (72.7%) had diminished ovarian reserve despite continued menstruation, previous studies that have only used menstrual history as a surrogate for ovarian reserve appear to have underestimated the impact of these cytotoxic agents.