Multiple sclerosis (MS) is the most common chronic immune-mediated disease which goes along with serious somatic and psychic symptoms. Whereas recent research rather focussed on the neurological symptoms of MS, there is nowadays an increasing interest among researchers in psychological symptoms of the disease. It is known that about half of the MS patients suffer from cognitive deficits, and that cognitive decline has a disadvantageous impact on lifestyle and quality of life in affected persons. So far, cognitive deficits in subjects with MS have been described as rather isolated, specific cognitive disturbances with otherwise intact intellectual abilities, while global deterioration of mental skills in terms of dementia is considered as being rather rare. In the present article, we describe cognitive domains which are typically impaired in subjects with MS and reflect on the question if the diagnosis of dementia might be underrepresented in MS patients due to several reasons (e.g., progression of cognitive deficits in the course of the disorder, adhering very closely to memory deficits as cardinal symptom of dementia, lack of longitudinal studies of cognitive performance levels). Furthermore, we recommend a multistage neuropsychological diagnostic procedure for clinical practice which aims at diagnosing cognitive deficits already in early stages of the illness. In so doing, practitioners may be able to offer adequate therapies to affected persons in all stages of the disorder in order to improve psychosocial functional levels.