Surgically treated patients with oral, head and neck cancer commonly develop mucositis during additional irradiation therapy. Oral mucosa inflammation other than irradiation is mostly caused by Candida albicans, yeast of Candida genus. This study evaluated possible connection between grades of oral mucositis and oral yeast profile in irradiated patients before, during and after irradiation. In 25 examined patients mucosits grades »0« to »2« before irradiation with 20% positive smears and only two different species of yeasts (C. krusei 4%, C. albicans 16%) during the irradiation changed into »0« to »4« and 36% positive smears with five different species of oral yeasts (C. albicans 12%, C. glabrata 12%, C. parapsilosis 4%, C. guilliermondii 4% and Saccharomyces cerevisiae 4%). Three weeks after irradiation was finished mucositis decreased into »1« to »3« with 20% positive smears and again only two species of yeasts (C. albicans 16%, C. guilliermondii 4%). Mucositis grades was increased significantly (p=0.0037) with changes in fungi profile.