Introduction. Actinomycosis is a disease caused by anaerobic Gramme positive bacterium Actinomyces israeli. This is a specific inflammation with characteristic pathomorphological changes (sulphur granules), which is accompanied by focuses of fibrosis and the formation of abscesses or fistulas. Actinomycosis may develop in any organ, but the most frequent localization involves face and neck (63%), lungs (15%) and abdominal cavity, including pelvis minor (22%). Regardless of the observed decrease in the total incidence of actinomycosis in recent years, the number of cases involving the abdominal cavity and pelvis minor localization in the population of women who use intrauterine contraceptive devices (IUD) has increased. Aim. To present, on the basis of own experience, a case of multiorgan actinomycosis within the pelvis minor, as a disease which is too rarely considered in the differentiating diagnostic process in cases of tumour originating from the reproductive organ, urinary tract or alimentary tract. Materials and methods. This article discusses a case of actinomycosis of the pelvis minor, involving the left ovary and tube, bladder, rectum, sigmoideum and pelvic wall. It describes the diagnostic process preceding the surgery, the surgery itself, during which an intraoperative histopathological examination was performed, facilitating the final diagnosis and the application of penicillin therapy. Diagnostic problems involving actinomycosis and a significant role of intraoperative histopathological examination are emphasised. The relationship between pelvic actinomycosis and the application of intrauterine contraceptive device is highlighted. Conclusions. 1. Clinical picture of actinomycosis localized in the reproductive organ may be similar to that of a neoplastic process. 2. In the case of tumours of the pelvis minor of non-specific localization, associated with the application of intrauterine device as a contraceptive method, the possibility of actinomycosis should be considered. 3 Histopathological examination, performed intraoperatively or by biopsy before the surgical procedure, is decisive in the diagnostic process and subsequent treatment. 4. The evaluation of a diagnostic value of bacteriological cultures taken from the uterine cervix to detect anaerobic bacteria in the female population with an increased risk of infection caused by Actinomyces israeli requires further research performed on a large group of patients. [ABSTRACT FROM AUTHOR]