The frequency of Cushing's syndrome (CS) in obese patients was not properly determined and the studies focused on the frequency of occult CS and the possible improvement of diabetes and obesity with treatment of CS are needed. In this study, we aimed to investigate the frequency of CS in obese patients with type 2 diabetes. The study enrolled with 200 obese (body mass index (BMI) > 30 kg/m(2)), type 2 diabetes patients between 2009 and 2011 in Sisli Etfal Training and Research Hospital, Turkey. Twenty-eight males and 172 females were recruited to the study. Mean age of the study group was 51.7 +/- 8.5. Nineteen patients (9.5 %) failed to suppress cortisol levels less than 1.8 mu g/dL after a 1-mg overnight dexamethasone suppression test (ODST) and these patients proceeded to have a 2-day 2-mg low-dose dexamethasone suppression test. After further screening, three (%1.5) patients were diagnosed with CS in our study. Among the three patients diagnosed with CS, the tumor was located in the pituitary gland in two patients. The present study revealed that the frequency of Cushing's syndrome in obese and diabetic patients were 1.5 %, which was much higher than the general population. Occult CS should take into account as an exacerbating factor for diabetes and screening for CS should be considered in poorly controlled diabetic patients.