This study presents the modern concepts of pathogenesis, risk factors, etiology, clinical manifestations, prevention, and treatment of oropharyngeal mucositis, one of the main complications of radiation therapy for head and neck region cancer. The leading role in the mechanisms of disease development belongs to rapidly dividing cells of the basal layer of the oropharyngeal mucous membrane. This damage is due to both direct (excitation and ionization) and indirect (accumulation of active oxygen and nitrogen compounds, activation of transcription factors, hyperfunction of pro-inflammatory cytokines, etc.) action of ionizing radiation on the most important biological molecules and supramolecular structures (polynucleotides, nucleoproteins, phospholipids, etc.). The main risk factors for mucositis include the localization and size of the tumor, the amount of radiation dose to the oral region, and individual body characteristics (young age, pernicious habits, metal structures of dentures, a history of periodontal disease, etc.). The disease severity is described from mild (erythema and moderate pain that does not require analgesia) to severe (ulceration, hemorrhage, necrosis, and other symptoms) to establishment necessary prescription of effective means of pathogenetic and symptomatic therapy. The main means and methods of prevention of radiation-induced mucositis include the following: non-steroidal anti-inflammatory drug benzydamine, means of protection against oxidative stress glutamine, and drugs with a complex stimulating effect on wound healing processes. Drug therapy for mucositis involves the use of benzydamine; the tricyclic antidepressant doxepin; and a gel consisting of polyvinylpyrrolidone (Belclaiz), mucolytic acetylcysteine. When non-narcotic analgesics are ineffective, low doses of opiates (fentanyl, morphine, and methadone) are used in oral, transdermal, or parenteral dosage forms, as well as low-intensity laser therapy. The most important components of the etiopathogenetic therapy of the disease include antiviral drugs (acyclovir and valacyclovir) and fungicides (clotrimazole, fluconazole, and itraconazole). Enteral nutrition difficulty indicates nasogastric or nasojejunal tube usage, and in more serious cases, surgical methods such as gastro- or jejunostomy.