With “checkpoint inhibitors” targeting PD1/PD-1-ligands or CTLA-4/CD28 pathways, immunotherapy has profoundly modified therapeutic strategies in oncology. First approved in refractory metastatic neoplasms (melanoma and lung adenocarcinoma), it is now being tested broadly in other cancers and/or as adjuvant treatment. For a significant proportion of patients, immunotherapy is responsible for “immunological” events, identified as Immune-Related Adverse Events (irAEs). Owing to the increasing number of prescriptions, identification and management of specific immunological side effects is crucial and requires close collaboration between oncologists and internists and/or other organ specialists. Within irAEs, we propose to individualize the induced autoimmunity by the term “Opportunistic Autoimmunity Secondary to Cancer Immunotherapy” (OASI). The aims of this article are (1) to present the different available checkpoint inhibitors and the OASIs reported with these treatments and (2) to propose practical recommendations for diagnosis, pre-therapeutic assessment and management of OASIs. The need for predictive biomarkers of OASIs occurrence will also be discussed.