Laparoscopic Roux-en-Y gastric bypass (RYGB) is widely applied in the treatment of morbid obesity. Health personnel meeting these patients should thus be familiar with the potential clinical consequences of the modified anatomy induced by the surgery. After a RYGB, the stomach is left in situ after the closure of the upper part of the organ. This blind-ended gastric remnant may cause complications and surgical emergencies, but also opportunities for diagnostic and therapeutic intervention. The present review focuses on complications related to the gastric remnant including bleeding and acute dilatation in the early postoperative period and later adverse events such as gastroduodenal peptic disease, tumors, gastrogastric fistulas, and late dilatation. Opportunities offered by the remnant, including minimal invasive or open access for enteral nutrition, and therapeutic and diagnostic access to the bile ducts, the duodenum, and the gastric remnant, which is challenged by the modified anatomy, are discussed. Reversal of the gastric bypass and gastrointestinal reconstruction after esophageal resection have been commented on. The review aims to improve the awareness of issues related to the gastric remnant for physicians involved in the treatment and the follow-up of patients after a RYGB.