The Fatigue Severity Scale (FSS) is a widely used instrument to measure the impact of fatigue on specific types of functioning. This study aims to translate and test the reliability and validity of the Portuguese version of the FSS. The questionnaire was administered to a worker sample of 424 nurses. Reliability analysis showed satisfactory results (Cronbach's alpha coefficient = .87). The test-retest reliability was .85. The principal component analysis showed that the FSS was a measure with a one-factor structure. The construct validity of the total FSS score was assessed by correlation with Maslach Burnout Inventory (MBI) score, Depression Anxiety Stress Scale (DASS) score, and Visual Analogue Scale (VAS) score. Each of the corresponding correlation coefficients among the total FSS score and MBI score, DASS score, and perceived fatigue score (VAS) were .55 (p < .01), .62 (p < .01), and .68 (p < .01), respectively, which shows sufficient construct validity. To measure the discriminant validity of FSS, we examined the differences in scores between groups in terms of the number of hours of sleep and overtime. The less nurses slept and the longer they worked, the higher their total FSS score became. This preliminary validation study of the Portuguese version of FSS proved that it is an acceptable, reliable, and valid measure of fatigue in the working population.
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