The effects of age, educational level, duration and course of the disease, physical disability and mood status on several cognitive functions (short- and long-term memory, frontal functions, attention, language and visuospatial skills) have been evaluated in 42 multiple sclerosis (MS) patients. The Hamilton Depression Rating Scale (HDRS) scores and a secondary progressive disease course significantly influenced neuropsychological performance. Factorial analysis revealed that indexes of (1) frontal function impairment, (2) long-term verbal memory and language function impairment, and (3) visuospatial short- and long-term memory and visuoperceptive function impairment accounted for 85% of the variance in neuropsychological performance. Only the first factor was significantly related to the presence of depressive symptomatology, as assessed by the HDRS. These results indicate that both the course of the disease and the presence of affective disorders must be taken into account when evaluating the natural history of cognitive impairment in MS and suggest that depressive symptomatology and cognitive dysfunction in MS are related to the involvement of at least partially overlapping anatomofunctional circuits.