Advances in our understanding of the regulatory mechanisms of the immune system have led to the development of novel approaches for cancer therapy, including inhibition of immune checkpoints with anti-CTLA-4 and anti-PD-1 antibodies. An increasing number of immunomodulatory treatments are under investigation, and are beginning to show promise in clinical trials. As more-effective therapies become available based on modulation of the immune system in order to trigger or enhance antitumour immune responses, clinicians will need to become familiar with recognizing and controlling the adverse effects arising from immune therapy. This Review describes the toxicity profiles for various anticancer therapies based on the use of agents that block immune checkpoints, immunostimulatory agents, and adoptive T-cell therapy (that is, infusion of modified autologous T cells). The management of patients receiving these treatments presents unique challenges for clinicians. Nevertheless, many of the adverse effects associated with these treatments are reversible and can be managed with supportive care either with or without cessation of therapy. This final point is extremely important given the continued development of new cancer immunotherapies, and the importance of safe and effective use of existing effective FDA-approved agents.