<p>Marginal ulcer (MU) is one of the most challenging complications following one anastomosis gastric bypass (OAGB), occurring in approximately 2.59% of patients, predominantly during the first year after surgery. The disease presents through a range of symptoms, including epigastric pain in most patients, and can culminate in serious conditions such as bleeding, perforation, or stenosis. Given the complexity of managing MU in the context of OAGB, especially in cases of revision, this systematic review and meta-analysis aimed to determine the incidence and treatment of MU after OAGB, as well as the outcome in both primary and revisional cases. According to PRISMA guidelines, this systematic literature search was conducted searching Web of Science, PubMed, Embase, and Scopus up to August 2024. We included randomized clinical trials (RCTs) as well as retro- and prospective cohort studies that measured MU following OAGB in adults for the meta-analysis and most relevant and considerable case reports/series for the systematic evaluation. To measure the incidence of post-OAGB MU and its management, meta-analyses were performed using random-effects models, taking into account heterogeneity (<i>I</i>²), and subgroup analyses were conducted based on surgery type, geography, study design, and follow-up duration. Sixty-six studies of 25,615 patients were analyzed. Overall pooled incidence of MU after OAGB was 2% (95% CI, 2–3%; <i>I</i>² = 86.37%). Subgroup analyses gave rates of MU of 3% (95% CI, 2–4%; <i>I</i>² = 83.58%) in primary OAGB and 2% (95% CI, 1–3%; <i>I</i>² = 28.50%) in revisional surgery. There was regional variation, and the MU rate in Europe was 3% (95% CI, 2–4%; <i>I</i>² = 88.07%) compared with 2% (95% CI, 1–2%; <i>I</i>² = 74.30%) in Asia. The majority of MU (69%; 95% CI, 56–81%; <i>I</i>² = 84.95%) were managed medically, most commonly using proton pump inhibitors (PPIs). Surgical interventions were utilized more commonly in refractory or complex situations. Meta-regression revealed a moderate correlation between increased follow-up and more medical treatment, and funnel plot analysis suggested potential publication bias. Among all the included studies, gastrointestinal bleeding was the most commonly reported. The leading complications, that required interventions, were perforation and bleeding. Smoking, followed by <i>Helicobacter pylori</i> (<i>H. pylori</i>) infection was the most commonly reported risk factors. MU remains a significant postoperative OAGB complication with a weighted incidence of 2%, found more frequently in primary rather than revisional cases. Medical treatment remains the foundation of its management, even if surgery does become necessary in more severe situations. This highlights standardized diagnosis and treatment protocols, especially for high-risk groups, and adequate follow-up periods for identifying and successfully treating MU.</p>