Background: The prevalence of obesity has increased globally and is associated with many comorbidities such as type 2 diabetes and fatty liver and cardiovascular diseases. Bariatric surgery is considered an effective intervention for achieving weight loss and controlling lipidemia and glycemia.Objectives: This Saudi retrospective observational study evaluates the clinical and biochemical benefits following bariatric surgery to obese diabetic patients.Methodology: After gaining ethical committee approval, data was collected from the patients' medical records at a tertiary medical center (King Fahad General Hospital, Al-Madinah Al-Munawwarah, Saudi Arabia). The total sample size was 61 patients, of whom 78.33% (n=48) had a body mass index (BMI) of 40 or greater (obese class III).Results: Following bariatric surgery, there were statistically significant reductions (p<0.001) in BMI and HbA1C (decreased from 45.53±7.791 kg/m 2 and 7.9±1.82% to 33.42±6.18 kg/m 2 and 6.06±1.35%, respectively, after surgery). Likewise, significant reductions (p<0.001) occurred to serum total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides that decreased from 234.4±26.7 mg/dl, 152.2±19.4 mg/dl, and 187.3±24.6 mg/dl to 158.4±17.3 mg/dl, 95.6±15.7 mg/dl, and 132.5±19.5 mg/dl, respectively. Interestingly, serum high-density lipoprotein (HDL) significantly increased (p<0.001) from 43.8±6.2 mg/dl to 52.3±4.6 mg/dl. Using the novel clinical therapeutic index, bariatric surgery decreased BMI by about 26.6%. Using the novel biochemical therapeutic index, bariatric surgery decreased HbA1C, serum total cholesterol, serum LDL cholesterol, and serum triglycerides by about 22.99%, 32.42%, 37.18%, and 29.26%, respectively, while serum HDL increased by about 19.4%. Conclusion: Bariatric surgery is an effective intervention for obese diabetic patients resulting in weight loss, better control of diabetes and hyperlipidemia, and the metabolic profile. It is also recommended in Saudi Arabia for the high prevalence of obesity and diabetes mellitus.