Little is known about the neural correlates of cognitive deficits in chemotherapy treated survivors of childhood cancer. We used event related fMRI to study working memory in childhood cancer survivors. Subjects underwent an n-back task to test working memory function. Patients showed reduced BOLD signal on correct responses compared to controls in the anterior cingulate, posterior cingulate, and sensory association cortices. Patients showed increased activation on error trials in the angular gyrus and superior parietal lobule. The affected brain regions are known to be involved in memory function, reward, motor planning and motivation.