ABSTRACT
Actinomycosis, rare in pelvic localization and a severe condition not well known to gynecologists, is an uncommon entity caused by anaerobic bacteria, Actinomycosis israelii. After trauma, surgery, or other infections that alter the host's mucosal barriers, these organisms advance to invade surrounding tissue and organs. The pelvic loculation of the disease generally presents as a pseudoneoplastic formation, so it is very difficult to make an accurate diagnosis initially. We experienced a pelvic and abdominal actinomycosis confirmed by pathology in a woman who had been wearing an IUD and complained fever, chill, headache for one month, and lower abdominal pain and palpable mass. This case illustrates the importance of considering the possibility of actinomycosis when we met a vague abdominal mass.