We have studied the prevalence of fibromyalgia syndrome (FMS) in patients with type 1 and type 2 diabetes mellitus (DM). Relationship with disease control of DM and the presence of FMS was also evaluated. We have studied 93 consecutive patients with DM (85 with type 2 DM and 8 patients with type 1 DM) followed in Diabetes Center. Single researcher took the history and did physical examination including manual tender point examination according to Manual Tender Point Survey instructions. For the diagnosis of FMS, 1990 American College of Rheumatology Classification Criteria for FMS was used. We measured patients' fasting blood sugar levels and HbA1c levels around the same time period. Patients were excluded from the study if they had any other serious disease, and if there was any history of drug use that interferes with the symptoms of FMS. Patients with rheumatoid arthritis (RA) were accepted as controls. FMS was found in 18% of patients with DM type 2 (no patients with FMS in type 1 DM group), in 34% of patients with RA. Female patients with DM type 2 had significantly higher FMS rates. Mean fasting blood sugar levels and mean HbA1c levels were not significantly different between type 2 DM patients with FMS and DM patients without FMS. In RA group, in RA patients without FMS, the use of steroids was significantly higher. We have found an increased prevalence rate of FMS in patients with DM type 2 and RA. There was no correlation between the prevalence rate of FMS and good DM disease control.