Fatty liver disease (FLD) can be a precondition for other liver pathology including cholangiocarcinoma(CCA). Diabetes mellitus (DM) has been suggested in some studies to be a risk factor for FLD as well as cancers,including cholangiocellular carcinoma; however, there are currently very few studies on FLD in DM subjects,although the rate of FLD continues to increase annually. To determine the association between DM and FLDultrasonographic data were analyzed from the Cholangiocarcinoma Screening and Care Program (CASCAP), innortheast Thailand. DM was reported by the subjects based on the CASCAP health questionnaire. Factors thatwere associated with FLD were determined by prevalence, odds ratio (ORs) and its 95% confidence intervals(CIs) using multiple logistic regression. There were 45,263 subjects with a mean age of 53.46 (±9.25) years. FLDwas found in 36.3% of DM subjects but only in 20.7% of non-DM subjects. The association between DM andFLD was adjusted for all other factors including gender, age, education level, relatives diagnosed with CCA,smoking, alcohol consumption, and hepatitis B and C. The risk of DM in subjects having FLD was highlysignificant compared with the non-DM subjects (OR 2.13; 95%CI: 1.92 to 2.35; p-value < 0.001). Thus DM issignificantly associated with FLD which in turn may facilitate the development of several diseases includingCCA. DM should be taken into consideration in future ultrasonic investigations of FLD and CCA.