Chimeric antigen receptor T-cell therapies are promising new options for patients with relapsed or refractory diffuse large B-cell lymphoma or acute lymphoblastic leukaemia. They increase complete response rates and the chances of achieving prolonged remission. Chimeric antigen receptor T cells are specially modified lymphocytes designed to stimulate the body's own immune system to target malignant cells. The process involves an initial harvest of the patient's own T cells, genetic modification, T-cell expansion and then reinfusion. Cytokine release syndrome is a major short-term complication of chimeric antigen receptor T-cell therapy. The presentation typically resembles septic shock and can be fatal. Immune effector cell-associated neurotoxicity syndrome is another major short-term complication. It presents with a spectrum of neurological deficits ranging from headache, delirium and anxiety to seizures and coma. There are early promising results with chimeric antigen receptor T-cell therapies in other cancers. These include mantle cell lymphoma, multiple myeloma and some solid organ tumours such as glioblastoma multiforme.