. Haemopoietic stem cells transpantation: a narrative review. Haematopoietic stem cell transplantation (HSCT) is an effective treatment for many haematological malignancies and its employment is growing thanks to the increased possibility of finding suitable donors and the discovery of therapies to treat major complications. The fourth contribution on emergencies in the oncology setting proposes a narrative literature review to describe the transplant pathway, the types of HSCT, the conditioning regimen, the stem cells reinfusion, the aplasia phase, the major complications and the follow-up. The review included secondary studies published from 2020 to 2022, on adult transplanted patients and written in English; 30 studies were included. In addition, 28 primary studies describing key issues and 11 textbooks were added. Both autologous and allogeneic HSCT expose patients to infectious or drug therapy-related complications, such as mucositis and bleedings. The allogeneic HSCT is at higher risk of major complications such as the graft-versus-host disease and the venous-occlusive disease. The update proposed is accompanied by two cases with multiple choice questions, in patients who underwent autologous stem cells hematopoietic transplantation: case 1 (published in this issue of the AIR journal) on septic shock and case 2 (which will be published in the next issue of the AIR journal) on a massive hemothorax.