Background. Despite the fact that M. hominis is commonly assigned to opportunistic microorganisms, there are many reports of clinical cases with the involvement of M. hominis as the only microorganism in the development of severe inflammatory processes in the lung, intervertebral discs, kidney, liver, heart, and brain. The role of M. hominis in the development of pelvic inflammatory diseases (PID) remains unexplored. Clinical case reports. The paper gives data on two patients admitted to hospital to be treated for tubo-ovarian abscess and pyosalpinx. The patients underwent a comprehensive examination, as well as laparoscopy, during which intraoperative samples were obtained and investigated by PCR to detect DNA of a broad spectrum of microorganisms. The material obtained from the two patients with PID displayed M. hominis DNA at a concentration of 108 GE/ml (that corresponded to total concentration of DNA of the bacteria that were present in the biomaterial). Other microorganisms were not found in one case; their concentration was 100 and more times lower than that of M. hominis in the other case. Conclusion. The most probable etiological role of M. hominis was established in two clinical cases of PID. The possible role of M. hominis in the development of PID should be taken into account when elaborating the tactics of examination and treatment for patients with this condition. © 2017, Bionika Media Ltd. All rights reserved.