Cognitive dysfunction may occur in some patients who receive chemotherapy. We provide a summary of an April 2003 workshop on this topic, that included medical oncologists, radiologists, clinical and experimental psychologists, and patient advocates. Current studies indicate that cognitive deficits are often subtle, although they are observed consistently in a proportion of patients, may be durable, and can be disabling. Deficits have been observed in a range of cognitive functions. Underlying mechanisms are unknown, although preliminary studies suggest there may be genetic predisposition and that cognitive impairment may be accompanied by changes in the brain detectable by neuroimaging. The following priorities were established for future research: (1) large-scale clinical studies that use both a longitudinal design and concurrent evaluation of patients with cancer who do not receive chemotherapy-such studies should address the probability and magnitude of cognitive deficits, factors that predict them, and underlying mechanisms; (2) exploration of discrepancies between subjective reports of cognitive dysfunction and the objective results of cognitive testing; (3) studies of cognitive function in patients receiving treatment for diseases other than breast cancer, and in both men and women, to address the hypothesis that underlying mechanisms relate to changes in serum levels of sex hormones and/or to chemotherapy-induced menopause; (4) development of interventions to alleviate these problems; and (5) development of animal models and the use of imaging techniques to address mechanisms that might cause cognitive impairment associated with chemotherapy.