Fatigue is one of the most frequent symptoms in multiple sclerosis (MS) but there is a lack of knowledge about its behaviour over time. The aim of our study was to investigate changes in fatigue in a large cohort of MS patients and to determine the relationship between changes in disability and depression with changes in fatigue severity.We studied fatigue in 227 MS consecutive patients and again after one year. During the clinical interview, we recorded the patient's degree of disability using the Expanded Disability Status Scale and relapses; fatigue was measured by means of the Modified Fatigue Impact Scale (MFIS) and Fatigue Severity Scale (FSS) and depression was measured by the Beck Depression Inventory (BDI).After a mean follow-up of 18 months, 86.8% of patients who were fatigued at study onset remained in a fatigued status, whereas 25% of those without fatigue at onset had become fatigued at the end of follow-up. We observed that only variations on BDI scores positively correlate with variations on fatigue scales, mainly with MFIS (r = 0.49, p < 0.0001). An increase of BDI score was the factor that best predicted the increase of fatigue over time. No differences in the increase of fatigue were found between patients with and without progression of disability during the follow-up period, or between patients with or without relapses.Fatigue in MS persists over time. Changes in mood status but not in disability are related to changes in fatigue in MS patients.