RecruitingDiagnostic testPolish Version Fatigue Severity ScaleFatigue is one of main symptoms in multiple sclerosis, amyotrophic lateral sclerosis and other diseases with profound effect on quality of life and professional and social functioning. Not infrequent it is misdiagnosed as sleepiness or other symptom. Fatigue severity scale is a time efficient and easy to apply instrument to assess the impact of fatigue on patient's life. The aim of this study is to validate the Polish-language version of the Fatigue Severity Scale.