A high incidence of ample diseases with a complicated etiology, including mycoses of various origins, determine the implementation of unconventional methods, including hirudotherapy, to their treatment. The study was aimed at assessing the mycological purity of medical leech body covers, their jaws and gastrointestinal systems – oesophagus, middle and posterior intestines, and the purity of water from an aquarium they were kept in. The experimental material were 20 European medical leeches (Hirudo medicinalis) and water originating from their breeding. Fungi were obtained according to our own procedures and mycological diagnostics was conducted following standard procedures applied in mycological laboratories. In total, 22 species of fungi belonging to 13 genera were isolated. The material studied was found to contain fungi classified as potential pathogens: Candida albicans, Candida guilliermondii, Candida krusei and Candida tropicalis, as well as numerous saprotrophs with a decreased pathogenicity potential. In view of the results obtained in this study, and a prospective application of hirudotherapy, a question may arise as to whether sterility of cultures and health status of leeches are sufficient and safe for patients. Isolation of a relatively high number of fungi considered pathogenic from leeches poses a potential hazard for people who could have contact with non-sterile therapeutic material, which in this case leeches are.