Introduction <p>Bariatric surgery is the most effective treatment for severe cases in obesity. However, the altered gastrointestinal anatomy after bariatric surgery can affect drug absorption, potentially leading to false-positive results in diagnostic tests. This study aims to evaluate the reliability of dexamethasone suppression test (DST) in post-bariatric surgery patients and explore how different bariatric procedures influence DST outcomes.</p> Methods <p>In this single-center, cross-sectional study conducted at the Obesity Center in tertiary university hospital. Patients who had undergone bariatric surgery, completed at least 9–12 months of postoperative recovery, and had a pre-operative DST were included the study. Sociodemographic and clinical data were obtained. All patients underwent an overnight DST and laboratory tests.</p> Results <p>Sixty-eight patients included study: 47 sleeve gastrectomy (SG), 21 Roux-en-Y gastric bypass (RYGB). Baseline weight and BMI were similar (<i>p</i> = 0.68, <i>p</i> = 0.873, respectively). At last follow-up, RYGB patients had lower weight compared to SG (<i>p</i> = 0.049). Postoperative DST levels showed no significant change in SG (<i>p</i> = 0.055), but increased significantly in RYGB (0.72 vs. 0.84; <i>p</i> = 0.028). Although postoperative DST values were higher in RYGB, the difference between groups was not significant (<i>p</i> = 0.196). A moderate positive correlation was found between pre- and postoperative DST values (<i>r</i> = 0.464, <i>p</i> &lt; 0.001), with no association between DST and sex, surgery type, BMI, or weight loss.</p> Conclusions <p>Despite potential alterations in absorption after bariatric surgery, the DST appeared to remain reliable and adequately suppressed cortisol in the majority of patients. Thus, our findings suggest that DST may be considered a safe and valid screening tool for Cushing’s syndrome in patients undergoing bariatric surgery.</p>