OBJECTIVES: The NIH roadmap project “Patient-Reported Outcomes Measurement Information System” (PROMIS) provides a basis for measuring symptoms - including fatigue; associated with chronic diseases.  However, information on use of PROMIS with Fibromyalgia (FM) patients is limited.  This study sought to evaluate the factor structure of the 95-item PROMIS Fatigue item bank among individuals with FM.  It is unknown whether the conceptual structure of fatigue experience (intensity, frequency, and duration) and impact (physical and mental) will be supported in individuals with FM. METHODS: An internet-based survey was conducted with individuals with FM.  Participants had to be ≥18 years and diagnosed with FM by a physician.  Respondents were randomized into one of three cohorts, each of which completed one-third of the 95-items from the entire PROMIS v1.0 Fatigue Item Bank (www.nihpromis.org).  Items were balanced between cohorts.  Item factor analysis was performed using both a polychoric correlation matrix with Mplus and a full-information approach using ORDFAC.  Comparisons were made using the Akaike Information Criteria (AIC) and Bayesian Information Criterion (BIC).  Models chosen based on BIC produced interpretable factors for assessment of the PROMAX rotated factor loadings. RESULTS: 1,207 respondents completed the survey.  Mean age of the respondents was 52.1 years.  Mean time since FM diagnosis was 8.7 years.  All groups produced factor structures that included 3 factors. The first consisted mainly of Fatigue Experience items.  The second consisted mainly of items related to Mental Impact and the third consisted of General Impact items. An additional factor related to Social Impact was identified in Group B only. CONCLUSIONS: For individuals with FM, the PROMIS Fatigue item bank appears to contain a factor structure that is consistent with the original PROMIS conceptual model.  Subscales from the PROMIS Fatigue item bank can likely be used to separate Fatigue Experience from General and Mental impacts of Fatigue.