An effect size analysis was used to review the neuropsychological literature of multiple sclerosis (MS) to determine whether reliable neurocognitive test deficits and differences between chronic-progressive and relapse-remitting subtypes are apparent. Studies dating back to 1983 were gathered and the neuropsychological test results from a total of 1,845 patients with MS, and 1,265 healthy controls, were synthesized using meta-analytic principles. The results indicate that neurocognitive impairment is indeed evident in patients with MS on a number of cognitive tasks and test variables. Secondly, distinct patterns of neurocognitive deficits are evident in chronic-progressive and relapse-remitting subtypes of MS. Finally, relations between neurocognitive impairment and clinical and demographic attributes of patients with MS were revealed.