Introduction. Tumor lysis syndrome is an emergency condition requiring prompt recognition and treatment. It?s a consequence of spontaneous or therapy-induced cellular death leading to the release of intracellular ions and metabolic products of purine bases into the bloodstream. Pathophysiology. The characteristic metabolic derangement comprises hyperkalemia, hyperphosphatemia, hyperuricemia, and hypocalcemia. These metabolic changes can lead to kidney failure, arrhythmia, and seizures. Epidemiology, classification and risk assessment. The incidence of tumor lysis syndrome varies between different types of tumors, but it is most common in hematologic malignancies. According to Cairo - Bishop Classification, tumor lysis syndrome can be defined as laboratory tumor lysis syndrome and clinical tumor lysis syndrome. Preventive measures and treatment of tumor lysis syndrome. Frequent laboratory monitoring is obligatory in patients with intermediate and high risk of tumor lysis syndrome. Preventive measures are based on vigorous hydration and administration of medication to control serum uric acid levels. When clinical tumor lysis syndrome develops, additional treatment, including renal replacement therapy, is needed for the correction of metabolic disturbances. Conclusion. Tumor lysis syndrome is a potentially fatal complication in patients with suffering from malignancies. Early recognition of patients at risk and administration of prophylactic and therapeutic measures improves outcomes for these patients.