OBJECTIVE To assess the different measure instruments used for patients with fibromyalgia. PATIENTS AND METHODS This study assessed 60 individuals participating in a clinical trial of cross-sectional cohort comparing the effects of exercises performed in water and on land. The following instruments were used: the Fibromyalgia Impact Questionnaire (FIQ) to assess the impact of the disease; the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) to assess quality of life; the Beck Depression Inventory to assess depression; and the Visual Analogue Scale (VAS) of pain. Those questionnaires were compared with the results obtained in a transitional Likert-type scale, the verbal scale for assessing change (VSAC), considered as a criterion of change in the assessment of other instruments. RESULTS The Spearman coefficient was used to study the correlation between the VSAC measure and the other instruments at two occasions (T1 and T2). At T1, a moderate correlation was observed between VSAC and VAS (r = 0.49), and between VSAC and FIQ (r = 0.41), and a negative correlation was observed between VSAC and the SF-36 domains pain (r = -0.49) and general health perception (r = -0.55), and the SF-36 physical component (r = -0.42). At T2, only the SF-36 domain vitality showed a weak negative correlation with VSAC (r = -0.27). CONCLUSION Considering VSAC as gold standard, none of the instruments assessed could optimally identify a change in the health status of patients with fibromyalgia.