Despite clinical reports of cognitive deficits associated with cancer chemotherapy, the underlying brain mechanisms are not clear. This research examined selective attention and working memory using functional magnetic resonance imaging (fMRI) in women before chemotherapy for localized breast cancer. Patients were tested with an established selective attention and working memory task during fMRI. Compared with healthy controls, patients showed (a) bilateral brain activation in high-demand task conditions with recruitment of additional components of attention/working memory circuitry, and (b) less accurate and slower task performance. Results indicate compromised cognitive functioning before any chemotherapy and raise key questions for further research.