The omega loop gastric bypass (OLGB) has become a very commonly performed bariatric procedure because of the advantages it carries over the Roux en Y gastric bypass (RYGBP). However, mini gastric bypass is a misnomer, as this procedure is more malabsorptive than the RYGBP. Recently, it is called single or one anastomosis gastric bypass. The omega loop procedure is associated with a risk of afferent loop syndrome, a known complication of the Billroth II (Finsterer) operation. This rare complication of the OLGB can be debilitating, serious, and deadly. Afferent loop syndrome should be suspected in case of malabsorption syndrome with chronic diarrhea, steatorrhea, iron-deficiency anemia, edema, emaciation, and osteomalacia and also in case of simple biological anomalies such as macrocytosis or megaloblastic anemia. The diagnosis can be confirmed by measuring bacterial overgrowth, although this requires a jejunal aspirate performed during endoscopy with jejunal intubation. A microbial population of more than 106 organisms per milliliter of aspirate is pathological. Afferent loop syndrome is encountered less frequently now that the number of gastrectomies has dropped. Yet, with the omega loop bypass procedure becoming more common, surgeons must again be made aware of this potential complication.