Immunotherapy delivered a new therapeutic option to the oncologist: Ipilimumab (anti-CTLA-4), Nivolumab and Pembrolizumab (anti-PD1), and Atezolizumab (anti-PD-L1) increase overall survival and show a better safety profile compared to chemotherapy in patients with metastatic melanoma, lung, renal cancer among others. But all that glitters is not gold and there is an increasing number of reports of adverse effects while using immune-checkpoint inhibitors. While chemotherapy could weaken the immune system, this novel immunotherapy could hyper-activate it, resulting in a unique and distinct spectrum of adverse events, called immune-related adverse events (IRAEs). IRAEs, ranging from mild to potentially life-threatening events, can involve many systems, and their management is radically different from that of cytotoxic drugs: immunosuppressive treatments, such as corticoids, infliximab or mycophenolate mofetil, usually result in complete reversibility, but failing to do so can lead to severe toxicity or even death. Patient selection is an indirect way to reduce adverse events minimizing the number of subjects exposed to this drugs: unfortunately PDL-1, the actual predictive biomarker, would not allow clinicians select or exclude patients for treatment with checkpoint inhibitors.