Background <p>Fibromyalgia is a complex syndrome affecting all dimensions of biopsychosocial health and quality-of-life. The aim of the study was to quantify the cross-sectional and longitudinal validity of single measurement scales in specific construct domains and to examine how they combine to build a comprehensive, multidimensional outcome assessment of fibromyalgia before and after a standardized interdisciplinary pain program.</p> Methods <p>This prospective cohort study assessed 123 patients using 8 measures: the Short Form 36 (SF-36), the Multidimensional Pain Inventory (MPI), the Symptom Checklist-90-Revised (SCL-90-R), the Quantification Inventory for Somatoform Syndromes (QUISS), the Fibromyalgia Health Assessment Questionnaire (FHAQ), the Fibromyalgia Impact Questionnaire (FIQ), the Coping Strategy Questionnaire (CSQ), and the 6-Minute Walking Distance (6MWD). The comprehensiveness of the constructs and their overlap were quantified cross-sectionally and longitudinally by bivariate correlations, explorative factor analysis, and effect sizes (ESs).</p> Results <p>The mean age of the participants was 48.6 years (+/-9.8); 86.2% were female. Factor analysis revealed 2 factors with a totally explained variance of 44.5%-64.5%. At the baseline and follow-up cross-sectional analyses, mental health and psychosocial factors loaded more strongly on the first, mental health factor, especially the 4 SCL-90-R scales (factor loads 0.75-0.90) than on the second, predominantly physical function factor. Longitudinally (score differences), the predominantly physical function factor was dominant, with loads of 0.61 (FHAQ), 0.66 (6MWD), and SF-36 and MPI pain (0.68 each). Maximum cross-sectional correlations were up to 0.89 between depression and anxiety, up to 0.87 between pain and interference on the MPI (0.79 longitudinally), and up to 0.83 between depression and catastrophizing. Longitudinally all scales showed improvements. The greatest effects were measured on MPI Pain severity (ES = 0.78) and Interference (0.71).</p> Conclusions <p>All 23 health parameters examined had moderate to high factor loads on at least one factor, evidence of the multidimensionality of fibromyalgia. Mental health and function explained the substantial, partially comparable variances of the clinical characteristics. Both domains are almost equally important in describing the syndrome. An accurate description of fibromyalgia requires comprehensive assessment of a broad spectrum of constructs, including fatigue, somatization and coping strategies, particularly catastrophizing, in addition to the traditional pain, function and mental health.</p>