The present study examined the extent and distribution of lymphocyte infiltration in demyelinated lesions in the cerebral cortex of multiple sclerosis (MS) patients. Tissue sections from the brain of 10 MS patients and five patients without neurological disease were double labeled for myelin basic protein and the lymphocyte markers CD3, CD4, CD8, CD45RO, and CD20. The highest density of CD3-positive T cells was found in MS white matter lesions (40.4/10 high power fields (hpf)). Fewer T cells were detected in cortical lesions that extended through both white and gray matter (12.1/10 hpf; P < 0.001). The lowest number of T cells was detected in intracortical demyelinated lesions (1.1/10 hpf). This was equal to the lymphocyte density in nondemyelinated cerebral cortex within the same tissue block (1.1/10 hpf) or cerebral cortex in control brains (1.8/10 hpf). A similar distribution was found using the CD4, CD8, and CD45RO markers. CD20-positive B cells were scarce in all specimens examined. These data indicate that areas of intracortical demyelination in chronic MS are not associated with an increased number of lymphocytes, or an altered distribution of lymphocyte subsets, when compared with control areas in MS and control patients. This finding indicates that the extent of lymphocyte infiltration in MS lesions is dependent on lesion location.