Oral mucositis is a common side effect of radiation therapy for head and neck cancer. Severe mucositis is followed by symptoms, such as extreme pain, mucosal ulceration and consequent limitations in swallowing and achieving adequate nutritional intake. Mucositis may also increase the risk of local and systemic infection and significantly affect quality of life and cost of care. Severe oral mucositis can lead to the need to interrupt or discontinue cancer therapy and thus may have an impact on cure of the primary disease. In spite of all the advances made in understanding the pathophysiology of oral mucositis, there is still no prophylactic therapy with proven efficacy and known risk factors. This review will discuss oral mucositis epidemiology, impact and side effects, pathogenesis, scoring scales and prevention.