BACKGROUND: Cognitive impairment (CI) may be present in people with multiple sclerosis (PwMS) in different stages of the disease, as well as in PwMS with various degrees of disability. This study aimed to investigate cognitive decline over a period of 12 months and to examine an association between cognition and the disability in PwMS, also over a period of 12 months. METHODS: The Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) battery was used, containing the Symbol Digit Modalities Test (SDMT), the Categorical Verbal Learning Test (CVLT), and the Brief Visuospatial Memory Test-Revised (BVMT-R). The Expanded Disability Status Scale (EDSS), Timed 25-Foot Walk (T25FW), and 9-Hole Peg Test (9-HPT) were used to assess the degree of disability. For the analysis of cognitive decline over the period of 12 months, Wilcoxon signed-rank test (paired sample t-test) was used. For the correlation between cognition and disability, Spearman's correlation test was used. RESULTS: We observed statistically meaningful difference only in one measure of cognition (CVLT), not the other two (SDMT and BVMT-R). SDMT significantly correlated with methods assessing the degree of disability in both time points. In the second examination, we observed a correlation between BICAMS and 9-HPT. Similarly, SDMT and BVMT-R also correlated with EDSS. CONCLUSION: To investigate the cognitive decline in PwMS, a longer period of time probably should have been chosen. EDSS is commonly used to monitor disease progression, but it does not include the evaluation of various parameters, such as cognition or upper limb function. Its use with the 9-HPT and cognitive tests may represent a more reliable and comprehensive assessment of a patient's clinical condition.