Populations of patients with strokes or tumors constitute the most frequently used subjects in neuropsychological research, and these populations are often combined when the investigation aims at establishing brain-behavior relationships. We compared these two populations with respect to their neuropsychological profiles. Seventeen subjects with tumors were individually matched to subjects with unilateral strokes on the basis of lesion location. Despite close matching of lesions, there were major differences in the neuropsychological impairments of the two groups, eg, all subjects with stroke in the left hemisphere had more severe language defects than did their counterparts with tumors, and some tumor subjects performed normally on all neuropsychological tests. These findings demonstrate that the cognitive and/or behavioral consequences of tumors or strokes in similar locations can be radically different. The two patient types should be treated separately for the purpose of neuropsychological research.