The incidence of malignant diseases has been rising with the extension of the human lifespan. On the other hand, the development of medicine and new treatments have contributed to the decrease in mortality rate. This results in the growing prevalence of malignant diseases in a general population. Consequently, we have encountered the growing number of patients exposed to the long-term process of oncological treatment which leads to the greater chance of emergency complications. Those can be the consequence of the cancer itself, its treatment or related to other comorbidities that can often be found in such patients. The emergencies in oncology are acute and life-threatening as well as directly or indirectly related to a malignant disease. They occur in patients who have already been diagnosed with cancer or as the early symptoms of a new cancer. The most common emergencies in oncology include four groups: metabolic states, hematological states, states caused by the growth and spread of malignant tumours and emergencies that are the side effects of medical treatments. While assessing a patient’s conditions, quick and efficient evaluation of his/her general condition, clinical image, disease stage and possible disease prognosis are requested. A quick and adequate therapy should be provided in order to decrease morbidity as well as mortality. Due to the increasing prevalence of malignant diseases in the future, it is expected that the majority of doctors (not only the specialists) will be trained to recognise the emergencies in oncology in order to instantly provide the best possible health care for their patients.