Multiple sclerosis (MS) subjects with diffusely abnormal white matter (DAWM) typically progress faster on physical disability scores. The impact of DAWM on cognitive measures is unknown. 50 MS participants had conventional MRI and cognitive tests of Trails Making Test, Working Memory, and Processing Speed. The presence of DAWM was not associated with worse cognitive performance. As DAWM is most commonly present in posterior regions of the brain, it may be that these cognitive tests were not sensitive to DAWM-associated pathology.