The symptoms of irritable bowel syndrome (IBS) are commonly seen in fibromyalgia (FM) patients. This study aimed to evaluate the effect of 5-hydroxytryptamin-4 receptor partial agonist (tegaserod) on the symptoms of FM among the patients who receive the medicine because of IBS. Forty-one female patients with IBS and constipation, which were subjects to tegaserod treatment, were examined by rheumatologist and 14 were found to suffer from FM. The fibromyalgia impact questionnaire (FIQ) and clinical examination were done before tegaserod treatment and 1 month after. The IBS status, the total FIQ score, the number of tender points and pain in tender points were lowered significantly after the treatment (p < 0.001 for all variables). The results of this pilot study provide the preliminary evidence that FM patients can benefit from treatment by 5-hydroxytryptamin-4 receptor partial agonist. Additional studies are needed to support this conclusion.