Background Multiple sclerosis (MS) is a chronic, progressive, and neurodegenerative central nervous system disorder. MS usually causes disability, cognitive deficiency, fatigue, and depression symptoms. Objectives To assess cognitive functions of people with MS (pwMS) and investigate the impact of depression, fatigue, and disability on cognitive functions. Methods We administered the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) battery to assess 200 pwMS. The Expanded Disability Status Scale (EDSS) was used to evaluate disability levels. Fatigue Severity Scale (FSS) and the Beck Depression Inventory (BDI) were used, respectively, for fatigue and depression levels. Results EDSS and FSS scores were significantly higher in those with a disease duration of 5 years or more. Those with the EDSS >= 4 were found to have lower BICAMS performances and higher FSS scores. There was a significant difference in Symbol Digit Modalities Test (SDMT) performances between the groups with and without fatigue (FSS >= 4 and FSS < 4, respectively). When depression and fatigue symptoms concur or in the existence of just one of them or none of them, significant differences in terms of SDMT performances have been shown. Conclusion The level of disability and fatigue adversely affects the cognitive functions of pwMS; depression has no significant effect. BICAMS that is specific for MS can be beneficial to assess the cognitive state of pwMS.