Immunotherapies, such as immune checkpoint inhibitors (ICIs), have significantly advanced the treatment of cancer and other conditions. However, these therapies can also cause immune-related adverse events (irAEs), which are unintended side effects due to their effects on the immune system of the treated patient. These effects can be classified as organ-specific or systemic, with the latter being of particular interest due to their potential overlap with systemic autoimmune diseases (SADs). Autoantibodies, which are proteins produced by the immune system that react with self components, are often used to diagnose and classify SAD. However, the diagnostic value of autoantibodies in the context of systemic irAEs (sirAEs) triggered by ICIs is not well understood. This review aims to evaluate the diagnostic value of conventional autoantibodies in the identification and classification of sirAEs. A comprehensive search of the literature was conducted using the PubMed database, with a focus on articles published in the past 10 years. The results of the review suggest that, although autoantibodies can be useful in the diagnosis and classification of some SAD triggered by ICIs, there is a clear predominance of seronegative irAEs. The lack of traditional autoantibodies may suggest a unique mechanism for sirAEs and increases the already complex diagnostic approach of these manifestations, requiring evaluation by multidisciplinary teams with extensive experience in immunomediated diseases. Further research is needed to fully understand the diagnostic value of autoantibodies in this context and to determine the optimal approach for their detection and interpretation.