This paper presents results of two studies conducted to investigate cognition in different MS subtypes. First, the results of a study that has previously been published will be discussed. This was a cross-sectional study with 108 relapsing-remitting (RR), 71 secondary progressive (SP), 55 primary progressive (PP) MS patients, and 67 healthy controls [S.C.J. Huijbregts, N.F. Kalkers, L.M.J. de Sonneville, V. de Groot, I.E.W. Reuling, C.H. Polman, Differences in cognitive impairment of relapsing-remitting, secondary and primary progressive MS. Neurology 63 (2004) 335-339]. The second study involved a follow-up assessment after 2 years and included 30 SPMS patients, 25 PPMS patients, and 33 controls. The Brief Repeatable Battery of Neuropsychological Tests (BRB-N) was used for all cognitive assessments. All patient groups demonstrated cognitive deficits compared to healthy controls. RRMS patients were less affected compared to patients with progressive MS subtypes on the Paced Auditory Serial Addition Task (PASAT) and the Symbol Digit Modalities Test (SDMT). These differences were attenuated after control for physical disability level as measured by the Expanded Disability Status Scale. RRMS and SPMS patients were more severely impaired than PPMS patients on the 10/36 Spatial Recall Task and Word List Generation. Results of the follow-up study indicated that both progressive MS subtypes showed a lack of improvement compared to controls on the PASAT and the SDMT, but not on the other tasks of the BRB-N, indicating that performance on tasks requiring multiple abilities concurrently, i.e. visuo-spatial ability and processing speed (SDMT) or working memory and processing speed (PASAT), is most likely to decline across time.