A recent gastric bypass can mask the symptoms of an acute abdomen. Physical examination is generally unreliable and subtle clinical symptoms or signs should alert clinicians to a significant postoperative problem. In morbidly obese patients, the presence of overt peritoneal findings is usually ominous, leading to sepsis, organ failure and death. We report a case of ruptured appendicitis following a laparoscopic Roux-en-Y gastric bypass. The patient developed tachycardia, fever, and leukocytosis in the absence of abdominal pain or positive upper GI contrast studies. Eventually, a CT scan revealed a large pelvic abscess and inflammation. A subsequent exploratory laparotomy confirmed a perforated appendicitis with pelvic peritonitis. Her recovery was rapid and uneventful. This case highlights the pitfalls in promptly diagnosing an unrelated acute surgical abdomen postoperatively in the morbidly obese patient. The need for extreme vigilance and a low threshold for aggressive intervention in the period after bariatric surgery is emphasized.