<p>Idiopathic inflammatory myositis (IIM, also known as idiopathic inflammatory myopathy) are a group of multisystemic diseases, including dermatomyositis (DM), antisynthetase syndrome (ASyS), immune-mediated necrotizing myositis (IMNM), inclusion body myositis (IBM), polymyositis (PM), and myositis overlap syndrome. Of these, DM is the most common form with an incidence of 6–10/100,000 inhabitants in Europe. The pathogenesis of IIM is complex and not yet fully understood. Using the example of DM, it has been shown that there is microvasculopathy with complement activation and immune complex deposition, which leads to endothelial damage and the release of various inflammatory mediators and von Willebrand factor antigen. Possible sites of manifestation include muscles, joints, skin, lungs, heart, and gastrointestinal tract, each with different symptoms. The frequency of clinical manifestation varies depending on the myositis subtype and on antibody (Ab) status. Using different antibody profiles, subclasses can be identified within the aforementioned IIM subtypes, within which patient clusters can be distinguished. The diagnosis of IIM is based on a combination of physical examination, laboratory analyses, imaging procedures, and histological findings. Based on defined high-risk factors such as adult DM, detection of NXP2 and TIF‑γ antibodies, age &gt; 40&#xa0;years, therapy-refractory course, dysphagia, and cutaneous necrosis, as well as intermediate risk factors, the malignancy risk can be estimated and an appropriate individual cancer screening can subsequently be performed. Due to a lack of evidence from high-quality therapeutic studies, treatment is mainly empirical, using steroids, immunosuppressants, rituximab, and cyclophosphamide.</p>