Case 1. A 40-year-old man, who underwent conservative therapy for complicated appendicitis 3 months earlier, was found to have persistent swelling of the appendix without inflammation on computed tomography (CT) before interval appendectomy. A type 2 tumor was found in the cecum obstructing the appendiceal orifice on colonoscopy. Radical ileocecal resection with lymph node dissection was performed for advanced carcinoma of the cecum. Case 2. A 42-year-old man was found to have persistent swelling of the appendix and enlarged lymph nodes along the ileocolic artery on CT three months after conservative treatment for complicated appendicitis. Colonoscopy showed an ulcerative lesion around the appendiceal orifice with the pathological diagnosis of adenocarcinoma of the appendix. Radical ileocecal resection with the small intestine was performed. In conclusion, the possibility of hidden malignancy of the cecum and appendix should be considered in cases of persistent morphological changes of the appendix without inflammatory changes at the follow-up imaging study before interval appendectomy, especially in patients over the age of 40 years.