Objective: Several studies have identified that adjuvant chemotherapy for breast cancer is associated with cognitive impairment; however, the magnitude of this impairment is unclear. This study assessed the severity and nature of cognitive impairment associated with adjuvant chemotherapy by conducting a meta-analysis of the published literature to date. Method: Six studies (five cross-sectional and one prospective) meeting the inclusion criteria provided a total of 208 breast cancer patients who had undergone adjuvant chemotherapy, 122 control participants and 122 effect sizes (Cohen's d) falling into six cognitive domains. First, the mean of all the effect sizes within each cognitive domain was calculated (separately for cross-sectional and prospective studies); second, a mean effect size was calculated for all of the effect sizes in each cross-sectional study; and third, regression analyses were conducted to determine any relationships between effect size for each study and four different variables. Results: For the cross-sectional studies, each of the cognitive domains assessed (besides attention) showed small to moderate effect sizes (-0.18 to -0.51). The effect sizes for each study were small to moderate (-0.07 to -0.50) and regression analysis detected a significant negative logarithmic relationship (R[squared]=.63) between study effect size and the time since last receiving chemotherapy. For the prospective study, effect sizes ranged from small to large (0.11-1.09) and indicated improvements in cognitive function from the beginning of chemotherapy treatment to 3 weeks and even 1 year following treatment. Conclusion: This meta-analysis suggests that cognitive impairment occurs reliably in women who have undergone adjuvant chemotherapy for breast cancer but that the magnitude of this impairment depends on the type of design that was used (i.e., cross-sectional or prospective). Thus, more prospective studies are required before definite conclusions about the effects of adjuvant chemotherapy on cognition can be made.