A meta-alysis was performed to quantify the magnitude and ture of the association between adjuvant chemotherapy and performance on a range of cognitive domains among breast cancer patients. A total of 27 studies (14 cross-sectiol, 8 both cross-sectiol and prospective, and 5 prospective) were included in the alyses, involving 1562 breast cancer patients who had undergone adjuvant chemotherapy and 2799 controls that included breast cancer patients who did not receive adjuvant chemotherapy. A total of 737 effect sizes (Cohen's d) were calculated for cross-sectiol and prospective longitudil studies separately and classified into eight cognitive domains.The mean effect sizes varied across cross-sectiol and prospective longitudil studies (ranging from ??1.12 to 0.62 and ??0.29 to 1.12, respectively). Each cognitive domain produced small effect sizes for cross- sectiol and prospective longitudil studies (ranging from ??0.25 to 0.41). Results from cross-sectiol studies indicated a significant association between adjuvant chemotherapy and cognitive impairment that held across studies with varied methodological approaches. For prospective studies, results generally indicated that cognitive functioning improved over time after receiving adjuvant chemotherapy. Greater cognitive impairment was reported in cross-sectiol studies comparing chemotherapy groups with healthy control groups. Results suggested that cognitive impairment is present among breast cancer patients irrespective of a history of chemotherapy. Prospective longitudil research is warranted to examine the degree and persisting ture of cognitive impairment present both before and after chemotherapy, with comparisons made to participants' cognitive function prior to diagnosis. Accurate understanding of the effects of chemotherapy is essential to eble informed decisions regarding treatment and to improve quality of life among breast cancer patients.