Background: Modern immunotherapy based on immune checkpoint inhibitors is an innovative treatment, which is already used in the treatment of a number of malignancies, and many other checkpoint inhibitors have been investigated in clinical trials. Monoclonal antibodies against CTLA-4 (cytotoxic T-lymphocyte antigen-4) and PD-1 (programmed cell death-1) or PD-L1 (programmed cell death-1 ligand) are the most commonly used agents. The side effects of these treatments are similar in nature to those of autoimmune diseases. Recently, increasing evidence has indicated that some adverse effects of immunotherapy are associated with the beneficial effect of this treatment. Purpose: The aim of this review was to summarize current knowledge of the association between the adverse effects of checkpoint inhibitors and the outcomes of patients treated with this therapy. Conclusion: The association between the effect of immunotherapy and the occurrence of adverse reactions has been identified in a number of studies. It has been best documented in patients with malignant melanoma, non-small cell lung cancer, and renal cell carcinoma. Many studies published so far are limited by the relatively low number of patients and their retrospective design, leaving many questions still unanswered.