Fibromyalgia and irritable bowel syndrome frequently coexist. In this study, we utilized a previously validated self-administered questionnaire to assess the prevalence of symptoms of bowel dysfunction and irritable bowel syndrome in 123 patients with fibromyalgia as compared to 54 patients with degenerative joint disease (DJD) and 46 normal controls. Ninety (73%) of the fibromyalgia patients reported altered bowel function as compared to 20 (37%) DJD patients and none of the normal controls (P less than 0.001). Ninety-nine patients (81%) reported normal alternating with irregular bowel pattern, and 77 (63%) had alternating diarrhea and constipation. In contrast, only 24 (44%) of DJD patients and six (13%) of controls had regular alternating with irregular bowel pattern and only 12 (22%) of the DJD patients and none of the healthy controls had alternating constipation and diarrhea (P less than 0.01). Other bowel dysfunction complaints noted in the fibromyalgia group were abdominal gas (59%), nausea (21%), diarrhea (9%), and constipation (12%). Seventy-nine (64%) fibromyalgia patients reported frequent abdominal pain that was stress-related 47% of the time. Laxative use was frequent in the fibromyalgia group (19%) and absent in the other two groups. Fifty percent of fibromyalgia patients, compared to 28% of DJD patients, felt that their bowel complaints were worse during exacerbations of their joint disease (P less than 0.05). In conclusion, patients with fibromyalgia have a high prevalence of gastrointestinal complaints that should be carefully assessed. If the diagnosis of IBS is confirmed, appropriate treatment may improve patients' symptoms, although this approach requires further study.