To assess the evolution of cognitive and psychosocial functioning in a cohort of childhood and juvenile multiple sclerosis (MS) cases after a mean period of 2 years had elapsed since baseline evaluation. In this cohort study, we used the same extensive neuropsychological battery with alternative versions of the tests assessing memory, attention/concentration, executive functions, and language. Fatigue and depression were also measured. An interview on school and daily living activities was obtained from the parents. The cognitive performance of the patients was compared with that of demographically matched healthy controls (HC). Fifty-six patients and 50 HC were assessed. At follow-up, criteria for cognitive impairment (failure on at least 3 tests) were fulfilled in 39 patients (70%) and 75% of the cases were classified as having a deteriorating cognitive performance. Changes were prominent in tests of verbal memory, complex attention, verbal fluency, and receptive language. In the regression analysis, the only significant predictor of cognitive deterioration was older age of the subject (odds ratio 1.9, 95% confidence interval 1.2-2.9, p = 0.003). Psychiatric disorders, most frequently depression, were diagnosed in 12 patients (30.5%). Fatigue was reported by 21% of the patients. MS negatively affected school and everyday activities in 30% to 40% of the subjects. Our findings confirm the importance of systematic assessment of cognitive and psychosocial issues in children and teens with MS. The progressive nature of the cognitive difficulties emphasizes the need for developing effective treatment strategies.