In this study, we present a case of Behcet's colitis that caused acute inflammation in the gallbladder and mimicked the clinical picture of an acute abdomen: severe right-sided abdominal pain, nausea, fever, and tenderness in the right hypochondrium, right flank, right loin, and right iliac fossa (RIF), with severely elevated white blood cell (WBC) count. The picture of acute acalculous cholecystitis and acute abdomen was resolved after three days of antibiotic therapy. Then, the pain mainly was localized in the right flank and loin, with mild pain in the right iliac fossa, with positive Rovsing's and psoas signs. The pain in the right flank, loin, and RIF dramatically subsided after initiating a low dose of steroid injections. The colonoscopy, which was performed after the marked improvement of the patient's general condition, showed large, deep ulcers with severe colitis in the proximal transverse colon and the ascending colon. There was no cobblestone appearance. The histopathology of the colonoscopic biopsy showed surface ulceration with marked inflammatory infiltrates, mainly neutrophils, and no granulomas were found. The acid-fast bacillus (AFB) test was reported negative. Detailed history-taking, repeated clinical examinations, laboratory studies, and careful interpretation of ultrasound (US) and contrast-enhanced computed tomography (CECT) findings may prevent unnecessary surgical interventions in such fragile patients and lead to a better prognosis. A diagnosis of Behcet's colitis was made, taking into consideration the patient's past medical history, mucocutaneous lesions, and US, CECT, colonoscopic, and histopathology findings. Although there are no specific investigations and tests for Behcet's colitis, sparing of the rectosigmoid area, the absence of cobblestone appearance, the presence of deep, large round ulcers, patchy localization of the lesions, the absence of granulomas, and negative AFB are helpful for confidently excluding other specific colitis such as Crohn's disease, ulcerative colitis, intestinal tuberculosis (TB), diverticulitis, and ischemic colitis. In our view, in the differential diagnosis of the non-surgical cause of acute abdomen, Behcet's colitis must be considered among other rare causes, such as inferior myocardial infarction, diabetic ketoacidosis, sickle cell disease, familial Mediterranean fever, and acute intermittent porphyria, especially for the population of Mediterranean coast and Middle East countries.