Fibromyalgia (FM) syndrome and irritable bowel syndrome (IBS) are functional disorders in which altered somatic and or visceral perception thresholds have been found. The aim of this study was to evaluate the prevalence of FM in a group of patients with IBS and the possible association of FM with patterns and severity of the intestinal disorder. One hundred thirty consecutive IBS patients were studied. The IBS was divided into four different patterns according to the predominant bowel symptom and into three levels of severity using a functional severity index. All patients underwent rheumatological evaluation for number of positive tender points, number of tender and swollen joints, markers of inflammation, and presence of headache and weakness. Moreover, patients' assessments of diffuse pain, mood and sleep disturbance, anxiety, and fatigue were also measured on a visual analogue scale. The diagnosis of FM was made based on American College of Rheumatology classification criteria. Nonparametric tests were used for statistical analysis. Fibromyalgia was found in 20% of IBS patients. No statistical association was found between the presence of FM and the type of IBS but a significant association was found between the presence of FM and severity of the intestinal disorder. The presence of FM in IBS patients seems to be associated only with the severity of IBS. This result confirms previous studies on the association between the two syndromes.