BACKGROUND: Electromagnetic-field therapy has beneficial short-term effects in multiple sclerosis (MS) patients with major fatigue, but long-term data are lacking. PRIMARY STUDY OBJECTIVES: To evaluate the long-term effects of a specific electromagnetic therapy device (Bio-Electromagnetic- Energy-Regulation [BEMER]) on MS-related fatigue, we designed a crossover control of a previously performed randomized controlled trial and a long-term open-label follow-up trial. DESIGN AND SETTING: Crossover and open-label follow-up trials at a single neurological outpatient center. PARTICIPANTS: Patients with relapsing-remitting MS who had major fatigue (N = 37 patients). INTERVENTION: After a previous randomized controlled trial (exposure to low-frequency pulsed magnetic fields for 8 min twice daily or to placebo treatment for 12 wk), a crossover from control to treatment for another 12 weeks, followed by an open label follow-up trial to 3 years, were done. PRIMARY OUTCOME MEASURES: The outcome criteria were the Modified Fatigue Impact Scale (MFIS), Fatigue Severity Scale (FSS), German long version of the Center for Epidemiologic Studies Depression Scale (CES-D), Multiple Sclerosis Functional Scale (MSFC), and Expanded Disability Status Scale (EDSS). RESULTS: Patients previously on placebo during the randomized controlled trial experienced significant reductions in fatigue after crossing over to treatment. The MFIS and FSS scores were significantly lower in the open-label group than in the control subjects after follow-up. Participation in the open-label treatment was the strongest predictor of low fatigue outcome after followup. Electromagnetic-field therapy was well tolerated. CONCLUSIONS: In this long-term study, a beneficial effect of long-term BEMER therapy on MS fatigue was demonstrated. Electromagnetic-field therapy may be a useful therapeutic modality in MS patients with severe fatigue.