PURPOSE: To demonstrate the radiologic characteristics of the pelvic actinomycosis. MATERIALS AND METHODS: We retrospectively reviewed the radiologic findings of seven patients with pathologically proven pelvic actinomycosis and analyzed the anatomical location, characteristics of the lesion and alteration of surrounding structures. RESULTS: The location of the lesions were the ovary and adnexa(n=4), rectum(n=1), cecum and terminalileum(n=1), and bladder(n=1). Three of the seven patients had a past history of intrauterine devices.Post-contrast enhanced CT showed an ill-defined mass with inhomogeneous enhancement and a tendency to invade th esurrounding normal tissue plane. CONCLUSION: Pelvic actinomycosis should be included in differential diagnosis when an unusually aggressive infiltrative mass is located in the pelvic cavity, especially in a patient with long-term use of intrauterine contraceptive devices.