Sixty patients, 46 with left-hemisphere strokes and 14 with right-hemisphere strokes, and 21 normal control subjects were tested for the ability to use syntactic structures to determine the meaning of sentences. Patients enacted thematic roles (the agent, recipient and goal of an action) in 12 examples of each of 25 sentence types, which were designed to test a wide variety of syntactic operations. Both right-and left-hemisphere damaged patients performed worse than control subjects on syntactically complex sentences, and left-hemisphere patients performed worse than right-hemisphere patients. Eighteen patients with left-hemisphere strokes underwent CT scanning to image the perisylvian association cortex. There was no difference between the performance of patients with anterior and posterior lesions, and no correlation between the degree of impairment and the size of lesions in different regions of the perisylvian cortex. These results are consistent with the view that syntactic processing involves an extensive neural system, whose most important region is the left perisylvian cortex. When these results are combined with those of other studies, the picture that emerges is one in which, within this cortical region, this system manifests features of both distributed and localized processing.