Acute cholecystitis is the inflammation of the gallbladder, classically caused by gall stones obstructing the cystic duct. In contrast, acalculous cholecystitis is a gallbladder inflammation occurring in the absence of cholelithiasis with a reported prevalence of 10% of all cases of acute cholecystitis. Reactive acalculous cholecystitis is an extremely rare subset of this disease that results from an adjacent inflammatory or infectious intra-abdominal process that may lead to gallbladder stasis, ischemia, and subsequent wall inflammation. Many factors have been associated with acalculous cholecystitis, including (but not limited to) hemodynamic instability, altered immunity, and biliary tree anomalies. Lack of specific signs and symptoms of this particular entity often delays the diagnosis. Herein, we present a rare case of acute, reactive, acalculous cholecystitis secondary to a perforated duodenal ulcer found incidentally during laparoscopic cholecystectomy.