PIP: Vesical actinomycosis, though rare, is being discovered more among women who use IUDs. The case study is presented of a 32 year old woman with actinomycosis of the bladder. An analysis of the disease reveals that human actinomycosis is caused primarily by actinomyces israeli. It grows anaerobically and a number of strains are micro-aerophilic. Infection can begin principally in 3 ways: 1) when endogenous actinomyces penetrate damaged tissues following trauma, 2) other infections of foreign bodies, or 3) surgical manipulation. Pelvic actinomycosis is now being seen in women with IUDs. Urinary tract infection seldom occurs, and kidneys are affected more than ureters or the bladder. In appearance, vesical actinomycosis resembles a retropubic mass. It is possible that female organs, when confronted by a foreign body, may make it possible for the development of a undetectable actinomycotic pelvic infection. Treatment for actinomycosis is extensive antibiotic therapy with penicillin, tetracycline, clindamycin, or erythromycin. Surgery may be necessary when the disease produces a large mass and there's a need to drain abscesses, or to extirpate sinus tracts.