Tumor lysis syndrome (SLT) is a rare and potentially fatal entity. It represents an oncological emergency. It can be diagnosed by its clinical presentation and also by laboratory results. In most cases it is presented as a complication of the chemotherapeutic treatment of oncohematological diseases with large tumor mass. Less frequently, a syndrome of spontaneous tumor lysis has been described, or secondary to the use of corticosteroids, hydroxyurea and radiotherapy. In its most severe forms it may require hospitalization in intensive care units and invasive therapeutic measures such as hemodialysis. We report four cases of SLT with unusual presentation characteristics admitted to our Medical Research Institute.