Cognitive dysfunctions are frequent symptoms in multiple sclerosis (MS). Up to 65% of MS patients suffer from cognitive dysfunctions. Especially memory, attention and executive functions are impaired. These problems strongly affect the patients' ability to work and their quality of life (QoL). A differentiating diagnostic effort is necessary to control fatigue and depression. Screening tools alone can not provide a detailed description of all cognitive domains. Therefore, an elaborated neuropsychological diagnostics is necessary. This report provides a description of cognitive functions and its diagnostic opportunities, especially in MS patients. After displaying aspects of differential diagnostics, a recommendation for a diagnostic work schedule is given.