Tumour lysis syndrome (TLS) is a life-threatening oncological emergency characterized by metabolic abnormalities including hyperuricaemia, hyperphosphataemia, hyperkalaemia and hypocalcaemia. These metabolic complications predispose the cancer patient to clinical toxicities including renal insufficiency, cardiac arrhythmias, seizures, neurological complications and potentially sudden death. With the increased availability of newer therapeutic targeted agents, such as rasburicase (recombinant urate oxidase), there are no published guidelines on the risk classification of TLS for individual patients at risk of developing this syndrome. We convened an international TLS expert consensus panel to develop guidelines for a medical decision tree to assign low, intermediate and high risk to patients with cancer at risk for TLS. Risk factors included biological evidence of laboratory TLS (LTLS), proliferation, bulk and stage of malignant tumour and renal impairment and/or involvement at the time of TLS diagnosis. An international TLS consensus expert panel of paediatric and adult oncologists, experts in TLS pathophysiology and experts in TLS prophylaxis and management, developed a final model of low, intermediate and high risk TLS classification and associated TLS prophylaxis recommendations.