The aim of this study was to compare the occurrence of prediabetes [impaired fasting glucose and/or impaired glucose tolerance are considered to be precursors to type 2 diabetes mellitus (DM)) in irritable bowel syndrome (IBS) cases and matched controls. Ninety-two patients with IBS and 104 healthy matched controls were included in this study. Type 2 DM was considered an exclusion criterion in both groups. Fasting blood glucose, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglyceride levels were examined; after I night of fasting, an oral glucose tolerance test with 75 g glucose was administered, and the blood glucose levels after 2 hours were examined. Although there were no significant differences in the triglyceride levels, significant differences were found for total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol levels (P < 0,001, 0.001, and < 0.001, respectively). These measures were found to be elevated in the IBS group compared with the control group. The frequency of prediabetes, which is regarded as the first stage of type 2 DM, was also found to be significantly higher in the IBS group (P < 0.001). After adjusting for potential confounders, such as age, lipid levels, and anthropometric measures in the analysis of covariance models, prediabetes was significantly more frequent in the IBS group than in the control group (P < 0.001). Thus, given the higher prediabetes occurrence in IBS, IBS may indirectly indicate a higher risk of DM. Further investigations will be necessary to fully elucidate the mechanisms behind these observations.