We assessed the different sets of diagnostic criteria for primary progressive multiple sclerosis (PPMS), in order to determine their sensitivity when applied to a cohort of 261 PPMS patients. According to the Thompson criteria, 168 patients (64.4%) had definite PPMS, 84 patients (32.2%) had probable PPMS, and nine patients (3.4%) had possible PPMS; according to the McDonald criteria, 180 patients (69%) had PPMS; according to the revised McDonald criteria, 194 patients (74.3%) had PPMS. Our findings indicate that the revised McDonald criteria are more sensitive than the original McDonald criteria, but less sensitive than the Thompson criteria.