BACKGROUND/AIMS: Colonic actinomycosis is a rare disease with clinical and radiographic findings that overlap those of other inflammatory and neoplastic conditions. We performed this study to analyze clinical manifestation, characteristic radiologic findings of 5 cases of abdominal actinomycosis, which was initially diagnosed as a colorectal cancer or periappendiceal abscess. METHODS: We analyzed chief complaint, predisposing factor, presence of leukocytosis and sulfur granule, involved site, presence of LN involvement and abdominal CT findings, retrospectively. RESULTS: The most common clinical manifestation was abdominal pain. In 3 cases, predisposing factors were identifiable, which were intrauterine contraceptive device (IUD), previous appendectomy, and diabetes mellitus (DM) respectively. Leukocytosis was noted in 4 cases (80%) and sulfur granule in all 5 cases. Sigmoid colon was the most common involved site (4 cases) followed by appendix and rectum. On computed tomography, inhomogeneous mass or severe inflammation along the bowel wall or serosa was noted. Explorations were performed in 4 cases. Preoperative diagnosis was a colorectal cancer in 3 cases and periappendiceal abscess in 1 case. CONCLUSIONS: Actinomycosis should be born in mind in the differential diagnosis of patients with IUD, previous appendectomy and DM, presenting leukocytosis and CT finding of inhomogeneous mass and relatively uncommon LN involvement to eliminate unnecessary explorations.