Objectives: To confirm that structured reporting of CT scans using ten signs in clinical practice leads to a better accuracy in diagnosing internal herniation (IH) after gastric bypass surgery, compared with free-text reporting. Methods: In this prospective study, CT scans between June 1, 2017, and December 1, 2018, were included from a cohort of 2606 patients who had undergone laparoscopic gastric bypass surgery between January 1, 2011, and January 1, 2018. The CT scans were made for a suspicion of IH and structured reports were made using a standardised template with ten signs: (1) swirl sign, (2) small-bowel obstruction, (3) clustered loops, (4) mushroom sign, (5) hurricane eye sign, (6) small bowel behind the superior mesenteric artery, (7) right-sided anastomosis, (8) enlarged nodes, (9) venous congestion, and (10) mesenteric oedema. Furthermore, an overall impression of IH likelihood was given using a 5-point Likert scale. CT scans performed in 2011 until 2017, without structured reporting, were included for comparison. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated using two-way contingency tables; the chi-square test was used for calculating p value. Reoperation and 3-month follow-up were used as reference. Results: A total of 174 CT scans with structured reporting and 289 CT scans without structured reporting were included. Sensitivity was 81.3% (95% CI, 67.7–94.8%) and 79.5% (95% CI, 67.6–91.5%), respectively (p = 0.854); specificity was 95.8% (95% CI, 92.5–99.1%) and 88.6% (95% CI, 84.6–92.6%), respectively (p = 0.016); PPV was 81.3% (95% CI, 67.7–94.8%) and 55.6% (95% CI, 43.3–67.8%), respectively (p = 0.014); NPV was 95.8% (95% CI, 92.5–99.1%) and 96.0% (95% CI, 93.5–98.6%), respectively (p = 0.909); and accuracy was 93.1% (95% CI, 88.0–96.2%) and 87.2% (95% CI, 82.7–90.7%), respectively (p = 0.045). Conclusion: Structured reporting for the diagnosis of internal herniation after gastric bypass surgery improves accuracy and can be implemented in clinical practice with good results. Key Points: • Ten signs are used to aid CT diagnosis of internal herniation after gastric bypass surgery. • Structured reporting increases specificity and positive predictive value and thereby prevents unnecessary reoperations in patients without internal herniation. • Structured reporting by means of a standardised template can help less experienced readers.