Currently, the interest in cognitive functioning following chemotherapy is rapidly expanding as is reflected in a growing number of published studies on this topic. Although most studies are indicative of cognitive deficits after chemotherapy, definite conclusions on the role of chemotherapy on cognitive function can often not be drawn due to methodological problems. On the basis of the studies on cognitive functioning after chemotherapy that are conducted in The Netherlands Cancer Institute, the current article describes a number of such methodological topics that obscure straightforward interpretation of neuropsychological findings in toxicity research. Measurement issues that diverge from usual assessment issues encountered in psychosocial oncology will be described, and factors that might play a role in the cause of cognitive impairment will be evaluated. Also, future developments necessary to gain more insight into the prevalence, the pattern, and the impact of cognitive problems following chemotherapy are discussed