Tuberculosis is a major public health problem worldwide. Tuberculosis can be confused with other diseases and its diagnosis is frequently delayed, especially in areas of low prevalence. Abdominal tuberculosis includes involvement of the gastrointestinal tract, peritoneum, lymph nodes, and/or solid organs; and accounts for 5% of all cases of tuberculosis. We report two cases of young patients who presented preoperatively as acute abdomen due to acute appendicitis. During surgery, these cases were misdiagnosed as "carcinomatosis", and in the postoperative period these cases were complicated with septic shock. In both cases, histopathology showed caseating granulomas which suggested tuberculous peritonitis and enteritis. Subsequently, RT-PCR in peritoneal fluid confirmed Mycobacterium tuberculosis. In one case the clinical response to treatment was excellent, and the other case was fatal. The aim of this report is to bring attention to the spectrum of tuberculosis, and to serve as a reminder of tuberculosis as the great imitator that can masquerade as cancer. Most tuberculous patients erroneously diagnosed as cancer have extensive "neoplastic" lesions that would suggest an advanced-stage malignancy. Assuming a case as an advanced cancer would reduce the chance of performing more exhaustive studies to get a definitive diagnosis and clinicians would be tempted to offer only palliative treatments.