OBJECTIVE: The importance of assessing fatigue in rheumatoid arthritis (RA) has been confirmed in numerous studies. Several instruments are available to assess fatigue, however, the psychometric properties of most have been determined in various populations other than RA and the instruments tend to measure different aspects of fatigue. The objective of this study was to assess the performance of two fatigue instruments, one was developed in the RA population and the other in a nondisease-specific population. METHODS: This study is an ongoing prospective, multi-center, observational study conducted to document long-term functional, clinical, humanistic and economic outcomes, and treatment patterns in patients with new onset rheumatoid arthritis. Two fatigue instruments were used to assess RA patients: The Functional Assessment of Chronic Illness Therapy- Fatigue Subscale (FACIT-F), an instrument used primarily in oncology populations, and the Multidimensional Assessment of Fatigue (MAF), developed in an RA population. MAF measures four dimensions of fatigue (severity, distress, degree of interference in daily activities, and timing). At baseline, patients were requested to complete both the 16-item, MAF and the 13-item, FACT-F via telephone interview. Using baseline data only, the correlation between the MAF and the FACIT-F was tested in 133 patients with early RA (signs and symptoms >3months and <12 months). RESULTS: Patients mean+SD age was 55+15 years and 77% were female. Mean+SD MAF score was 23.3+12.3 with a normal range of 1(no fatigue)-50(fatigue). Mean FACIT-F score was 33.2+9.3 with a normal range of 52 (no fatigue)-0 (fatigue). The aggregate scores for each instrument were highly correlated with a Pearson's coefficient of -0.81 (p<0.001). CONCLUSION: Based on this analysis, it appears that the FACIT-F has validity for use in the early RA population. However, as follow-up assessments are completed, a more detailed analysis may reveal additional psychometric properties of the instrument in the early RA population and with disease progression.