The aim of the study was to investigate the validity and reliability of the Turkish version of the fatigue severity scale (FSS) in fibromyalgia (FM) patients. Sixty-one FM patients and 54 healthy controls were evaluated using the Turkish version of the FSS. Reliability was investigated using test-retest reliability and internal consistency. Concurrent validity was evaluated between the FSS score and the VAS fatigue. Convergent validity was assessed by comparing the FSS score with the scores of VAS pain, Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Fibromyalgia Impact Questionnaire (FIQ). Spearman's rank correlation coefficient was used to evaluate validity. Test-retest reliability and internal consistency of the FSS were excellent in FM patients (ICC: 0.94, Cronbach's alpha coefficient: 0.85) and in the healthy controls (ICC: 0.90, Cronbach's alpha coefficient: 0.91). For the concurrent validity, the correlation between the FSS and VAS fatigue was very good in FM group (r: 0.63, P: 0.000) and in the healthy controls (r: 0.94, P: 0.000). For the convergent validity, correlations between the FSS and BDI, BAI, FIQ, pain intensity were moderate to good in both groups (P: 0.000). The Turkish version of the FSS has been proved to be valid and reliable to detect severity of fatigue in FM patients. We recommend the use of it in clinical practice. © 2010 Springer-Verlag.