Functional magnetic resonance imaging (fMRI) was used to determine whether performance on lexical tasks was correlated with cerebral activation patterns. We found that such relationships did exist and that their anatomical distribution reflected the neurocognitive processing routes required by the task. Better performance on intramodal tasks (determining if visual words were spelled the same or if auditory words rhymed) was correlated with more activation in unimodal regions corresponding to the modality of sensory input, namely the fusiform gyrus (BA 37) for written words and the superior temporal gyrus (BA 22) for spoken words. Better performance in tasks requiring cross-modal conversions (determining if auditory words were spelled the same or if visual words rhymed), on the other hand, was correlated with more activation in posterior heteromodal regions, including the supramarginal gyrus (BA 40) and the angular gyrus (BA 39). Better performance in these cross-modal tasks was also correlated with greater activation in unimodal regions corresponding to the target modality of the conversion process (i.e., fusiform gyrus for auditory spelling and superior temporal gyrus for visual rhyming). In contrast, performance on the auditory spelling task was inversely correlated with activation in the superior temporal gyrus possibly reflecting a greater emphasis on the properties of the perceptual input rather than on the relevant transmodal conversions. Hum. Brain Mapping 19:155–169, 2003. © 2003 Wiley-Liss, Inc.