BACKGROUNDObesity may also develop due to a viral infection caused by adenovirus 36. We aimed to detect the presence of neutralizing antibodies against Ad-36 in adult patients who developed type 2 diabetes due to obesity (BMI ≥ 30 kg/m2).METHODSThe patient group (PG) was composed of 80 obese people with type 2 diabetes, the patient control group (PCG) was composed of 40 non-obese people with type 2 diabetes, and the healthy control group (HCG) was com-posed of 40 non-obese people without type 1 or type 2 diabetes in this case-control study. The presence of Ad-36 neutralizing antibodies was studied by serum neutralization assay.RESULTSA significant difference was found between the PG and HCG in terms of Ad-36 antibody positivity (p < 0.0001) but no significant difference was detected between the PG and the PCG (p > 0.05). BMI, serum leptin, adiponectin, and triglyceride levels were significantly higher in the PG (p < 0.05). Conversely, TNF-α and IL-6 levels were significantly lower in the PG (p < 0.0001). When the two groups were compared, the mean levels of total cho-lesterol and LDL in the PG were found to be high, although not significant (p > 0.05). In type 2 diabetes patients (n = 120), age, BMI, HDL, LDL, triglyceride, total cholesterol, Ad-36 presence, leptin, adiponectin, TNF-α, and IL-6 parameters were taken as independent variables for logistic regression. While BMIs was found to be significant (odds ration [OR] = 2.358; p = 0.0001, 95% Cl 1.507 - 3.690, Ad-36 presence was found to be a significant (OR = 27.352; p = 0.003, 95% Cl 3.157 - 236.961). Our study showed that BMI and Ad-36 increase type 2 diabetes risk by 2.3 and 27.3-fold in the PG and PCG (type 2 diabetes patients) versus the HCG. There was also a significant difference between PCG and HCG.CONCLUSIONSWe suggest that Ad-36 seropositivity is also a risk factor for the development of type 2 diabetes independent of being obese.