OBJECTIVES: Fatigue has been reported by patients as an important symptom of rheumatoid arthritis (RA) and recommended for measurement in clinical trials. The objective was to evaluate the validity of, ‘WORST level of fatigue (weariness, tiredness) during the past 24 hours,’ item of the Brief Fatigue Inventory (BFI Q3) in a sample of US patients with self-reported RA. METHODS: 50 adults with RA were recruited to complete questionnaires at baseline and one week later. Internal consistency reliability of the BFI fatigue severity subscale (questions 1-3) was evaluated using Cronbach’s α. BFI Q3 was assessed using Intraclass Correlation Coefficient (ICC) for test-retest reliability; Pearson’s correlation coefficient for convergent validity with BFI fatigue severity subscale and Multidimensional Assessment of Fatigue (MAF) global score; and analysis of variance for known-groups discriminant validity with self-reported RA severity (mild, moderate, severe) and general health (very good, good, fair, poor). RESULTS: Participants were 76% female, 72% Caucasian, mean age (SD) 49.4(13.2) years and mean disease duration 13.7(12.0) years. Mean BFI Q3 score was 7.3(1.9) at initial and 6.8 (2.3) at retest; ICC=0.58. Correlation with fatigue severity subscale and MAF were r=0.79(p<.001) and r=.02(p=.92), respectively. Cronbach’s α for severity subscale =0.84. Mean BFI Q3 scores were 6.0, 7.1 and 7.8 (p=.36) and poor general health were 5.6, 7.0, 7.9, and 9.0 (p=.01), respectively. CONCLUSIONS: In a small sample of patients with RA, assessment of worst fatigue severity as measured by BFI Q3 demonstrated validity.  Discrimination based on RA severity was not significant, possibly due to low study power, however trended in the hypothesized direction. Test-retest reliability was low but acceptable, and expected due potentially to the episodic nature of fatigue. Further validation of the BFI Q3 in a larger sample is needed to confirm these findings that the measure is useful in the context of RA clinical trials.