Four cases of actinomycosis involving the uterus and adnexal structures are reported. In 2 cases the infection was transmitted from a ruptured appendix. Ascending actinomycosis involving the endometrium and resulting in adnexal abscesses was associated with the use of an IUD in 2 patients. This infection should be suspected in any patient who develops a pelvic abscess with an IUD in place. Culture and histologic examination of tissue removed with the IUD may be a means of early diagnosis. The nature of these infections became apparent only after serious complications developed. Each patient required several surgical procedures. The diagnosis remained unsuspected until repeated laboratory examinations detected the fungus. The difficulty encountered identifying Actinomyces israeli indicates the infection is often undetected. Gallium scans were helpful in localizing occult abscesses in 2 patients.