Objectives: To identify the concepts contained in treatment outcomes of randomized controlled trials (RCTs) for interventions in patients with fibromyalgia (FM) using the International Classification of Functioning, Disability, and Health (ICF) as external reference. Methods: RCTs between 1992 and 2001 were located in MEDLINE and selected according to predefined eligibility criteria. The outcome measures were extracted and the concepts within the outcome measures were identified and linked to the ICF using a content-analytical approach. Results: Forty-two trials on FM were included. Twenty-seven different questionnaires were extracted. Of all, 79.2% (N=236) of the clinical and physiologic outcomes could be linked to 31 different ICF categories and 84.7% (N=964) of the concepts contained in the health-status questionnaire to 113 ICF categories. Conclusions: The ICF provides a useful external reference to identify the concepts contained in outcome measures used in RCTs in FM.