Case 1) A 21-year-old Thai woman, and Case 2) a 22-year-old Indonesian woman, were each given a diagnosis of pulmonary tuberculosis. Immediately after starting medication, peritonitis symptoms appeared. Colonoscopies detected multiple rings and zonal ulcers. Abdominal tuberculosis was diagnosed, and anti-tubercular therapy was effective. Case 3) A 23-year-old man was given a diagnosis of pulmonary tuberculosis. The day after starting anti-tubercular therapy, he complained of abdominal pain that increased with muscular defense. He was given a diagnosis of perforation of the digestive tract, underwent emergency surgery, and recovered. Pathological examinations revealed granuloma with caseous necrosis and Mycobacterium tuberculosis. Physicians should be aware that tuberculosis can be a potential source of acute abdomen in young adults who do not take proper care of their health.