PURPOSE: The aim of this paper is to explore the current theories about definition, classification, incidence and physiopathology of osteoradionecrosis (ORN) of the jaws. Moreover, it is discussed the predisposing and risk factors for the development of osteoradionecrosis based on the literature review. DISCUSSION: Osteoradionecrosis is one of the most serious oral complications of head and neck cancer treatment. Osteoradionecrosis is a severe delayed radiation-induced injury, characterised by bone tissue necrosis and failure to heal. Osteoradionecrosis either stabilises or gradually worsens and is notoriously difficult to manage. The most widely accepted theory to explain its cause until recently was the theory of hypoxia, hypovascularity and hypocellularity. A new theory for the pathogenesis of osteoradionecrosis was proposed. The clinical presentations of osteoradionecrosis are pain, drainage and fistulation of the mucosa or skin that is related to exposed bone in an area that has been irradiated. The tumour size and location, radiation dose, local trauma, dental extractions, infection, immune defects and malnutrition can predispose its development. CONCLUSIONS: A better understanding of risk factors for the development ORN and of the underlying pathophysiology may improve our ability to prevent this complication and help to improve the prognosis for those being treated for osteoradionecrosis.