OBJECTIVES: To investigate the reliability and validity of the Spanish version of the 2010 American College of Rheumatology (ACR) Preliminary Diagnostic Criteria for Fibromyalgia (FM) in patients with chronic pain. METHODS: The 2010 ACR Preliminary Diagnostic Criteria for FM were adapted to a Spanish version following the guidelines of the Rheumatology Spanish Society Study Group of FM. Based on the 1990 ACR classi cation criteria for FM, patients with chronic pain were initially divided into two groups: a FM group and another group of non-FM individuals. Patients from the FM group were evaluated by tender points (TP) examination, Fibromyalgia Impact Questionnaire (FIQ), Widespread Pain Index (WPI), and Symptom Severity Scale (SSS). The non-FM (control) group included patients with rheumatoid arthritis (RA) and osteoarthritis (OA). They were evaluated by WPI and SSS. RESULTS: We included 1,169 patients divided into two groups: FM group (n=803; 777 women and 26 men) and non-FM group (n= 366; 147 patients with RA, and 219 with OA). The median value of TP and FIQ in the FM group was 16 and 74 respectively. The preliminary 2010 ACR criteria were met by 665 (82.8%) FM patients and by 112 (30.6%) patients from the non-FM group (p<0.0001). Statistically signi cant differences in the number of TP (p<0.03), FIQ (p<0.0001), WPI (p<0.0001) and SSS (p<0.0001) were observed when FM patients fulfilling the 2010 ACR criteria were compared with the remaining FM patients who did not fulfill these criteria. Sensitivity of the Spanish version of the 2010 ACR criteria was 85.6% (95%CI: 83.1-88.1), speci city 73.2% (95%CI: 68.4-78), positive predictive value 87.7% (95%CI: 85.3-90.1) and negative predictive value 69.4% (95%CI: 64.5-74.2). CONCLUSIONS: Our results indicate that the 2010 ACR Preliminary Diagnostic Criteria for FM may be useful to establish a diagnosis of FM in Spanish individuals with chronic pain.