Fibromyalgia (FM) syndrome is a disabling clinical condition of unknown cause, and only symptomatic treatment with limited benefit is available. Gluten sensitivity that does not fulfill the diagnostic criteria for celiac disease (CD) is increasingly recognized as a frequent and treatable condition with a wide spectrum of manifestations that overlap with the manifestations of FM, including chronic musculoskeletal pain, asthenia, and irritable bowel syndrome. The aim of this report was to describe 20 selected patients with FM without CD who improved when placed on a gluten-free diet. An anti-transglutaminase assay, duodenal biopsy, and HLA typing were performed in all cases. CD was ruled out by negative anti-transglutaminase assay results and absence of villous atrophy in the duodenal biopsy. All patients had intraepithelial lymphocytosis without villous atrophy. Clinical response was defined as achieving at least one of the following scenarios: remission of FM pain criteria, return to work, return to normal life, or the discontinuation of opioids. The mean follow-up period was 16 months (range 5-31). This observation supports the hypothesis that non-celiac gluten sensitivity may be an underlying cause of FM syndrome.