Although fatigue is a frequent complaint of patients with multiple sclerosis (MS), little is known about the origins of multiple-sclerosis-associated fatigue. Our primary focus was to study if the extent of cerebral abnormalities, as shown on magnetic resonance imaging (MRI), had any relation with the frequency and intensity of fatigue complaints of patients with a definite diagnosis of MS. Fatigue severity was rated by the patients with the use of a 2-week diary and a fatigue questionnaire, while conventional T1- and T2-weighted MRI provided several measures for cerebral abnormalities. In total, 72% of 45 patients reported to be seriously fatigued at least several times a week over the last 3-month period. Fatigue severity was not related to the total extent of cerebral abnormalities, or to MRI-based atrophy measures. Regional lesion load did not differ between fatigued and non-fatigued subjects. Although neurological disability, as measured by the Expanded Disability Status Scale (EDSS) and Neurological Rating Scale (NRS), did correlate significantly with most MRI measures, it showed no relation with fatigue severity. Neurological progression rates and number of exacerbations in the 2-year period prior to assessment were not significantly associated with the fatigue measures. Therefore, our findings suggest that differences in levels of self-reported fatigue in patients with multiple sclerosis cannot merely be explained by the degree of clinical disease activity, neurological disability or the extent of MRI abnormalities. These results are compared to other research findings and the possible role of alternative factors influencing fatigue in multiple sclerosis are discussed.